transfusion theory exam (weeks 7-12)

Antibodies can be found in blood, extravascular fluid and secretions → TRUE or FALSE?

TRUE

Why?

• Antibodies are produced by plasma cells & distributed throughout the body to provide immune protection

  • Blood: Antibodies circulate to recognise foreign antigens

  • Extravascular fluid: Mainly IgG protects surrounding tissues

  • Secretions: Mainly IgA protects mucosal surfaces

In newborn blood group testing, only the forward group technique is used → TRUE or FALSE

TRUE

Why?

• Anti-A & Anti-B antibodies are absent at birth and they only appear 10-15 days after birth

Blood group AB is known as the universal recipient → TRUE or FALSE

FALSE

Why?

• Blood group AB-RhD (pos) is known as a universal recipient

ABO blood group phenotype frequencies;

• O and AB have the lowest frequency

• O is the most frequent (46%)

• A1 is the most frequent (46%)

• A2 has the lowest frequency (2.3%)

• A & B have a similar frequency

O is most frequent (46%)

Why?

• Blood group O is the most frequent (46%) and the A1B blood group has the lowest frequency (2.3%)

From the two subgroups of the A blood group, only A1 react strongly with the anti-A reagent → TRUE or FALSE

FALSE

Why?

• Both A1 and A2 subgroups react strongly with the anti-A blood grouping reagent

Secretor status;

• The secretor gene consists of only one allele responsible for the expression of the H antigen

• The secretor gene consists of 2 alleles responsible for the expression of A & B antigens on RBCs

• The secretor gene consists of 2 alleles responsible for the expression of Glucosamine on RBCs

• The secretor gene consists of 2 alleles responsible for the expression of the H antigen

The secretor gene consists of 2 alleles responsible for the expression of the H antigen

Why?

• The secretor gene (FUT2) has two alleles: Se (dominant) & se (recessive)

  • SeSe or Sese: Secretor - produces H substance in secretions, allowing A/B substances to be expressed depending on ABO type

  • sese: Non-secretor - does not express ABH substances in secretions

*Secretor status determines ABH antigen expression in secretions (e.g., saliva), not on RBCs. H antigen expression on RBCs is primarily controlled by FUT1

Blood group antigens are generally found in serum, and antibodies (directed towards blood group antigens) found on cells → TRUE or FALSE

FALSE

Why?

• Blood group antigens are generally found on cells, and antibodies found in serum

Forward group/ing refers to the identification of:

• Antibodies in an individual’s plasma with commercially available reagents

• Antibodies on an individual’s red cells with commercially available reagents

• Antibodies in an individual’s plasma using the patient’s own red cells

• Antigens on an individual’s red cells with commercially available reagents

Antigens on an individual’s red cells with commercially available reagents

Why?

• The forward group identifies A & B antigens on RBCs using known antisera (anti-A & anti-B)

  • Agglutination (+): Antigen is present

  • No agglutination (-): Antigen is absent

ABO genes encode for

• Transferases that add a sugar moiety to pre-formed H substance

• A, B or O antigens (direct gene products)

• Transferases that add a sugar moiety to pre-formed A, B or O substance

• Transferases which add a protein moiety to pre-formed H substance

Transferases that add a sugar moiety to a pre-formed H substance

Why?

• ABO genes encode glycosyltransferases (enzymes) that add specific sugars to the H antigen on RBCs, determining blood group

  • A gene: Adds N-acetylgalactosamine → A antigen

  • B gene: Adds galactose → B antigen

  • O gene: Produces a non-functional enzyme → H antigen remains unchanged

*ABO genes encode enzymes, NOT the A & B antigens directly

If no H substance = Bombay blood group, but the individual may have A and B genes that produce a transferase → TRUE or FALSE?

TRUE

Why?

• The Bombay blood group (Oh) occurs when an individual cannot produce the H antigen on their RBCs due to the hh genotype

  • H antigen: Required as the precursor for A & B antigens

  • A/B genes: May still be present & produce functional transferases

  • Without H antigen: Transferases cannot form A or B antigens, even if the genes are present

• Therefore, Bombay individuals appear as group O on routine forward ABO grouping despite potentially carrying A or B genes

A person with blood type A can receive blood from which of the following donors?

• Only type A

• Only type B

• Types A and AB

• Types A and O

Types A and O

Why?

• Individuals with blood group A have A antigens on their RBCs & anti-B antibodies in their plasma

  • Type A: Compatible because its RBCs have A antigens

  • Type O: Compatible because its RBCs have neither A nor B antigens

  • Types B & AB: Incompatible because their B antigens react with the recipient’s anti-B antibodies, causing haemolysis

Which blood type is considered the universal donor?

• A

• B

• AB

• O

O

Why?

• Blood group O is considered the universal red blood cell donor because its RBCs lack both A & B antigens

  • Type O: No A or B antigens → minimises ABO incompatibility

  • Type A, B & AB: Have A and/or B antigens that may react with recipient antibodies

*O RhD negative is the universal RBC donor type when considering both ABO & RhD

What is the genotype of an individual with blood type AB?

• AA

• BB

• AB

• OO

AB

Why?

• Blood group AB has the genotype I^AI^B, where both A & B alleles are codominant

  • A allele: Produces A antigens

  • B allele: Produces B antigens

  • Codominance: Both alleles are expressed equally, resulting in both A & B antigens on RBCs

What type of antibodies does a person with blood type B have in their plasma?

• Anti-A antibodies

• Anti-B antibodies

• Both anti-A and anti-B antibodies

• No antibodies

Anti-A antibodies

Why?

• Individuals with blood group B have B antigens on their RBCs & anti-A antibodies in their plasma

  • B antigens: Recognised as self, so anti-B antibodies are not normally produced

  • A antigens: Recognised as foreign, so anti-A antibodies are naturally present

If a father is blood type A and mother is blood type B, what blood types could their offspring have?

• A and O

• A, B, and AB

• A, B, AB, and O

• B and O

A, B, AB and O

Why?

• A father with blood type A can have genotype AA or AO, while a mother with blood type B can have BB or BO

• If the father is AO & the mother is BO, their offspring can inherit any of the four ABO blood groups

• According the table in the image, each blood group has a 25% probability if both parents heterozygous (AO x BO)

Which blood type is known as the “universal recipient”?

• A

• B

• AB

• O

AB

Why?

• Blood group AB is the universal red blood cell recipient because individuals have both A & B antigens on their RBCs but neither anti-A nor anti-B antibodies in their plasma

  • Type A: Can receive A & O RBCs

  • Type B: Can receive B & O RBCs

  • Type AB: Can receive A, B, AB & O RBCs

  • Type O: Can receive only O RBCs

What happens if a recipient receives blood with an incompatible ABO type?

• No adverse effects

• Haemolysis (destruction of red blood cells)

• Mild fever

• Enhanced oxygen transport

Haemolysis (destruction of red blood cells)

Why?

• An ABO-incompatible RBC transfusion causes the recipient’s anti-A or anti-B antibodies (mainly IgM) to bind to the donor RBC antigens

  • Antigen-antibody binding: Recipient antibodies attack incompatible donor RBCs

  • Complement activation: IgM strongly activates the complement system

  • Intravascular haemolysis: Donor RBCs are destroyed within blood vessels, potentially causing a life-threatening acute haemolytic transfusion reaction

Interpret the following blood group reactions

Interpretations?

• Row 1: Anti-A, Anti-B & Anti-A/B pos; Anti-D neg. No anti-A or anti-B in plasma

• Row 2: Anti-B & Anti-A/B pos; Anti-D pos. Anti-A present in plasma

• Row 3: No A or B antigens; Anti-D pos. Both anti-A & anti-B present in plasma

• Row 4: Anti-A & Anti-A/B pos; Anti-D neg. Anti-B present in plasma

What defines the ABO blood group system?

The ABO blood group system is defined by the presence or absence of A & B antigens on the surface of RBCs (see table for layout)

What are the enzymes that confers carbohydrate specificity?

Glycosyltransferases
Why?

• Glycosyltransferases are enzymes that add specific sugars to the H antigen, determining ABO blood group specificity

  • A transferase: Adds N-acetylgalactosamine → A antigen

  • B transferase: Adds galactose → B antigen

  • O allele: Produces no functional transferase → H antigen remains unchanged

What carbohydrates define ABO blood group antigens?

ABO blood group antigens are determined by specific terminal sugars attached to the H antigen on RBCs

• A antigen = N-acetylgalactosamine (GalNAc)

• B antigen = D-galactose

• H antigen = L-fucose

• O group = H antigen remains unmodified

What ABO antigens are expressed on red blood cells?

ABO antigens are carbohydrate structures on the surface of RBCs, determined by the individual’s ABO blood group (see table for layout)

*H antigen is also present in varying amounts on normal A, B & AB red cells

What ABO antibodies are present in serum?

ABO antibodies are naturally occurring antibodies (mainly IgM) directed against the A or B antigens an individual lacks (see table for layout)

How do we undertake ABO blood grouping in the laboratory?

ABO blood grouping involves two complementary tests using haemagglutination:

1. Forward grouping: Patient RBCs are tested with anti-A & anti-B reagents to detect A & B antigens

2. Reverse grouping: Patient plasma is tested with known A₁ and B reagent RBCs to detect anti-A & anti-B antibodies

• Agglutination (+) indicates an antigen-antibody reaction. Forward & reverse grouping results must agree to confirm the ABO blood group

How do we determine what ABO blood groups can be used for donors & recipients?

ABO compatibility is determined by ensuring the recipient’s plasma antibodies do not react with antigens on the donor’s RBCs, preventing haemolysis (check table for RBC transfusion compatibility)

Why?

• Group O: Universal ABO RBC donor because RBCs lack A & B antigens

• Group AB: Universal ABO RBC recipient because plasma lacks anti-A & anti-B antibodies

• Group A: Cannot receive B antigens due to anti-B

• Group B: Cannot receive A antigens due to anti-A

RhD negative phenotype is most common in:

• Asians

• Africans

• None of the above

• Caucasians

Caucasians

The haplotype DCe (R1) is most frequent in:

• English

• None of the above

• Nigerians

• Chinese

Chinese

The 2 Rh genes, RHD and RHCE, are located on chromosome 1 and are very different in their sequence homology → TRUE or FALSE

FALSE

Why?

• The 2 Rh genes, RHD and RHCE, are located on chromosome 1 and are very similar in their sequence homology (94% similarity)

D antigen expression varies in number with different genotypes; Co-expression of C decreases the expression of D → TRUE or FALSE

TRUE

Why?

• The no. of D antigens expressed on RBCs varies depending on the individual’s Rh genotype

  • D antigen density: Different Rh genotypes express different no. of D antigens

  • C antigen co-expression: Can reduce D antigen expression, particularly when C is inherited in trans to D (on the opposite chromosome)

  • RhD status: Reduced D antigen density does not necessarily mean the individual is RhD neg

A patient that has developed Anti-D and Anti-C antibodies would need to be transfused with blood with the following haplotype:

• dce

• DCE

• dCe

• DcE

dce

Why?

• A patient with anti-D & anti-C antibodies must receive donor RBCs that lack both D & C antigens to prevent haemolytic transfusion reactions

  • dce: Lacks D & C antigens → Compatible

  • DCE: Contains D & C → Incompatible

  • dCe: Contains C → Incompatible

  • DcE: Contains D → Incompatible

*Lowercase d represents the absence of the D antigen, not an actual d antigen

An individual with the following haplotype ‘DCe’ may develop antibodies towards:

• E antigen only

• E and C antigens

• E and C antibodies

• c antigen only

• D antigens

E and c antigens

Why?

• The DCe haplotype (R₁) expresses three Rh antigens: D, C & e

  • D = Present → Normally no anti-D

  • C = Present → Normally no anti-C

  • e = Present → Normally no anti-e

  • E = Absent from this haplotype → May develop anti-E

  • c = Absent from this haplotype → May develop anti-c

• Therefore, an individual lacking E & c antigens may develop anti-E & anti-c antibodies following exposure through transfusion or pregnancy

*Both inherited haplotypes determine the complete Rh phenotype, in this case, assuming the other haplotype also lacks E & c

Antibodies towards the Rh antigens are high immunogenic. The order of immunogenicity includes (from highest to lowest):

• e > c > E > C > D

• D > E > c > C > e

• D > c > E > C > e

• D > E > e > C > c

D > c > E > C > e

*Immunogenicity refers to an antigen’s ability to stimulate an immune response & antibody production

k is highly immunogenic with low frequency of the antigen in the general population and therefore many individuals can make Anti-k antibodies → TRUE or FALSE?

FALSE

Why?

• k is highly immunogenic with high frequency of the antigen in the general population and therefore only approx. 0.2% or less of individuals can make Anti-k antibodies

About the Duffy blood group system:

• Mostly fixes complement

• Elute well in the acid glycine technique

• The antigens are poorly developed at birth

• React best in the indirect antiglobulin test

React best in the indirect antiglobulin test

Why?

• Duffy antibodies (anti-Fy^a & anti-Fy^b) are predominantly IgG antibodies that react best at 37°C & are detected during the IAT (AHG) phase

  • IgG antibodies: Usually produced following transfusion or pregnancy

  • IAT: IgG antibodies reacting with RBC antigens

  • Complement: Duffy antibodies usually do not fix complement

  • Enzymes: Ficin, papain & bromelain destroy Duffy antigens

  • Clinical significance: Can cause haemolytic transfusion reactions (HTRs) & occasionally HDFN

Kidd antigens;

• Poorly developed at birth

• Significance long life-time antibodies are produced against Ags

• Are only present on the red cells

• Antibodies show dosage

Antibodies show dosage

Why?

• Kidd antibodies (anti-Jk^a & anti-Jk^b) demonstrate the dosage effect, meaning they react more strongly with RBCs expressing a homozygous antigen than with a heterozygous antigen

  • Homozygous (Jk^aJk^a) → Stronger reaction with anti-Jk^a

  • Heterozygous (Jk^aJk^a) → Weaker reaction with anti-Jk^a

  • Clinical significance → Kidd antibodies can become undetectable over time & cause delayed haemolytic transfusion reactions (DHTRs)

The Rh system genes are:

• RHD and RHCE

• RHD and LW

• RHD and RHAG

• RHCE and RHAG

RHD and RHCE

Why?

• The Rh blood group is controlled by two closely linked genes on chromosome 1:

  • RHD gene: Encodes the RhD protein, responsible for D antigen expression

  • RHCE gene: Encodes the RhCE protein, responsible for C, c, R & e antigen expression

• Both genes determine the five major Rh antigens involved in transfusion compatibility

What type of molecules are Rh antigens?

• Glycophorins

• Simple sugars

• Proteins

• Lipids

Proteins

Why?

• Rh antigens are non-glycosylated transmembrane proteins found on the surface of RBCs

  • RHD gene → Encodes the D antigen

  • RHCE gene → Encodes the C, c, E & e antigens

  • Function → Help maintain RBC membrane integrity & may contribute to ammonium transport

• Unlike ABO antigens, which are carbohydrates, Rh antigens are proteins

Rh antibodies are primarily of which immunoglobulin class?

• IgA

• IgD

• IgG

• IgM

IgG

Why?

• Rh antibodies are primarily IgG immunoglobulins, produced following exposure to foreign Rh antigens through transfusion or pregnancy

  • IgG → Reacts best at 37°C & is detected using the Indirect Antiglobulin Test (IAT)

  • Crosses the placenta → Can cause haemolytic disease of the fetus & newborn (HDFN)

  • Extravascular haemolysis → IgG-coated RBCs are predominantly destroyed by macrophages in the spleen

  • Clinical significance → Can cause haemolytic transfusion reactions (HTRs)

An individual has the following serological reactions: D+C+E+c+e+. What is the most probable genotype?

• R₀R₁

• R₁r

• R₁R₂

• rr

R1R2

Why?

• The patient’s phenotype is D+C+E+c+e+, meaning all five major Rh antigens are present on their RBCs

• The R₁R₂ genotype consists of two haplotypes:

  • R₁ = DCe → Expresses D, C & e

  • R₂ = DcE → Expresses D, c & E

• Together, they express D, C, E, c & e, matching the patient’s serological results

Outline the difference between ABO & Rh antibodies

Indicate the expected reactions for the following blood groups

Key: + = agglutination; 0 = no agglutination

\*Bombay phenotype does not determine RhD status, so Anti-D may be pos or neg

\**A₂ individuals may produce anti-A₁, resulting in a pos reaction with A₁ cells, although most do not

Why?

• O pos → No A/B antigens; anti-A & anti-B in plasma; D antigen present

• AB neg → Both A/B antigens; neither anti-A nor anti-B; D antigen absent

• B pos → B antigen; anti-A in plasma; D antigen present

• Bombay → Lacks H antigen on RBCs, preventing A/B expression. Plasma typically contains anti-A, anti-B & anti-H, which reacts strongly with O cells

• A₂ RhD neg → Expresses A antigen with reduced A antigen density compared with A1; has anti-B in plasma; D antigen absent

Based on the forward & reverse grouping results (see image), the patient has the following blood group:

• O RhD negative

• B RhD positive

• A RhD positive

• O RhD positive

• AB RhD positive

O RhD positive

Why?

• No A or B antigens on the red blood cells and anti-A and anti-B antibodies in plasma; D antigens present on red cells → O RhD positive

Anti-M and anti-N antibodies are usually of clinical significance because they are usually IgM antibodies that can cross the placenta → TRUE or FALSE

FALSE

Why?

• Anti-M and anti-N antibodies are not usually of clinical significance because they are usually IgM antibodies that cannot cross the placenta & work best in the cold

Zeta potential is defined as the:

• Repulsive force generated by the negative charges on the erythrocyte surface

• Attracting force generated by negative & positive charges on the erythrocyte surface

• Repulsive force generated by positive charges on the erythrocyte surface

• Repulsive force generated by negative charges on the thrombocyte surface

Repulsive force generated by negative charges on the erythrocyte surface

Why?

• RBCs have a negative surface charge, primarily due to sialic acid on their membranes

  • Negative charges → Cause RBCs to repel each other

  • Zeta potential → The electrical potential associated with this surface charge, contributing to RBC repulsion

  • Agglutination → Reducing zeta potential allows RBCs to move closer together, making antibody-mediated agglutination easier

Antibodies to the ABO blood group system generally can be best detected:

• At very high pH levels (i.e. pH 10-11)

• At 37 degrees

• At very low pH levels (i.e. pH 2-3)

• At room temperature

At room temperature

Why?

• ABO antibodies are predominantly IgM antibodies, which generally react strongly at room temp

  • IgM → Reacts well at room temp

  • IgG → Generally reacts best at 37 degrees

  • ABO antibodies → Can also react at 37 degrees & cause severe haemolytic transfusion reactions

IgG antibodies characteristically react optimally at 37 degrees, but usually cannot cause agglutination in NaCl at room temperature → TRUE or FALSE?

TRUE

Why?

• IgG antibodies react optimally at 37 degrees, but usually cannot directly cause RBC agglutination in saline (NaCl) at room temp

  • IgG → Small, monomeric antibodies that generally cannot bridge the gap between RBCs due to zeta potential

  • Zeta potential → Negative surface charges cause RBCs to repel each other

  • AHG (Anti-Human Globulin) → Bridges IgG-coated RBCs, allowing visible agglutination in the antiglobulin test

Screening cells are always blood group:

• AB

• O

• A

• B

O

Why?

• Antibody screening cells are always group O RBCs because they lack A & B antigens, preventing interference from naturally occurring anti-A & anti-B antibodies

  • Group O cells → Lack A & B antigens

  • Prevents interference → Anti-A & anti-B will not react with screening cells

  • Purpose → Allows detection of unexpected RBC antibodies, such as anti-D, anti-K & anti-Jk^a

Sample labelling for blood banking test must include:

• Full name, UR or DOB, signature of person taking the blood, date of sampling

• Full name, UR or DOB, signature of person taking the blood, date and time of sampling

• A first name and surname

• A first name, surname & date of birth (DOB)

• A first name, surname & UR number

Full name, UR or DOB, signature of person taking the blood, date and time of sampling

All negative anti-human globulin (AHG) test results needs to be confirmed/checked with AHG control cells to identify:

• None of the above

• If the washing steps were performed

• All of the above

• If the red cells were washed adequately

• If the patient’s plasma was added

All of the above

Why?

• AHG control cells (Coombs check cells) are IgG-coated RBCs added after a negative AHG test to confirm that the negative result is valid

  • Adequate washing → Ensures unbound IgG has been removed so it cannot neutralise AHG

  • Active AHG reagent → Confirms AHG was added & remains functional

  • Positive agglutination → Check cells must agglutinate to validate the negative AHG result

  • No agglutination → Indicates an invalid test that must be repeated

*Little wonky cause technically AHG control cells cannot reliably confirm that the patient’s plasma was added. They primarily validate AHG activity & adequate washing

Papain reduces the zeta potential and increases the reactivity of some antigen-antibody complexes, but also DESTROYS some antigens (Ags) → TRUE or FALSE?

TRUE

Why?

• Papain is a proteolytic enzyme that modifies RBC surface proteins, reducing zeta potential & allowing RBCs to move closer together, enhancing certain antigen-antibody reactions

  • Reduces zeta potential → Decreases RBC repulsion, facilitating agglutination

  • Enhances antigens → Rh, Kidd, Lewis & P1 antigen-antibody reactions

  • Destroys antigens → Duffy (Fy^a, Fy^b) & certain MNS antigens (M, N, S, s)

Conclusive evidence of antibody identity (from an antibody panel) occurs when reactivity with 2 antigen-positive cells is shown and no reactivity with 2 antigen-negative cells → TRUE or FALSE

FALSE

Why?

• Conclusive evidence of antibody identity (from an antibody panel) occurs when reactivity with 3 antigen-positive cells is shown and no reactivity with 3 antigen-negative cells

Which blood group system is associated with resistance to P. vivax?

• Rh

• Kell

• Duffy

• Kidd

Duffy

Why?

• The Duffy blood group system is associated with resistance to Plasmodium vivax malaria because Duffy antigens act as receptors for parasite invasion of RBCs

  • Duffy antigens (Fy^a/Fy^b) → Can act as receptors for P. vivax

  • Duffy-null phenotype [Fy(a-b-)] → Lacks Duffy antigen expression on RBCs, providing strong resistance to P. vivax invasion

  • Clinical significance → Duffy antibodies (mainly IgG) can cause haemolytic transfusion reactions & HDFN

Which antibody is most commonly associated with delayed haemolytic transfusion reactions?

• Anti-s

• Anti-k

• Anti-D

• Anti-Jk^a

Anti-Jka

Why?

• Anti-Jk^a (Kidd blood group system) is strongly associated with delayed haemolytic transfusion reactions (DHTRs)

  • Antibody evanescence → Kidd antibodies can decrease to undetectable levels over time

  • Anamnestic response → Re-exposure to Jk^a-positive RBCs triggers rapid antibody production

  • Delayed haemolysis → Newly produced antibodies destroy transfused RBCs, typically days after transfusion

Which of the following best describes MN antigens and antibodies?

• Well developed at birth and susceptible to enzymes

• Poorly developed at birth and susceptible to enzymes

• Well developed at birth and not susceptible to enzymes

• Poorly developed at birth and susceptible to enzymes

Well developed at birth and susceptible to enzymes

Why?

• The M & N antigens (MNS blood group system) are well developed at birth but are sensitive to proteolytic enzymes

  • Well developed at birth → M & N antigens are expressed on fetal & neonatal RBCs

  • Enzyme-sensitive → Papain & ficin destroy M & N antigen activity

  • Antibodies → Anti-M & anti-N are usually naturally occurring IgM antibodies that react best at room temp

  • Clinical significance → Usually insignificant, although some IgG anti-M antibodies can cause HDFN or haemolytic transfusion reactions

Which antigen is destroyed by enzymes?

• P1

• K

• Fya

• Jka

Fya

Why?

• Duffy antigens (Fya & Fyb) are destroyed by proteolytic enzymes such as papain & ficin

  • P1 → Enzyme-enhanced

  • K (Kell) → Generally unaffected by enzymes

  • Fya (Duffy) → Destroyed by enzymes

  • Jka (Kidd) → Enzyme-enhanced

Which of the following characteristics best describes Lewis antibodies?

• IgM, naturally occurring, cause HDFN

• IgM, naturally occurring, do not cause HDFN

• IgG, cause haemolytic transfusion reactions

• IgG, do not cause haemolytic transfusion reactions

IgM, naturally occurring, do not cause HDFN

Why?

• Lewis antibodies (anti-Le^a & anti-Le^b) are predominantly naturally occurring IgM antibodies

  • IgM → Generally cannot cross the placenta

  • Naturally occurring → Usually develop without prior transfusion or pregnancy

  • HDFN → Do not cause HDFN because IgM cannot cross the placenta & Lewis antigens are poorly developed on fetal RBCs

  • Clinical significance → Usually insignificant, although rare haemolytic transfusion reactions can occur

The MNS blood group system is located on which chromosome?

• Chromosome 1

• Chromosome 4

• Chromosome 7

• Chromosome 19

Chromosome 4

Why?

• The MNS blood group system is controlled by genes located on chromosome 4

  • GYPA gene → Encodes glycophorin A, carrying M & N antigens

  • GYPB gene → Encodes glycophorin B, carrying S & s antigens

  • GYPE gene → Also contributes to genetic variation within the MNS system

Which of the following antigens is NOT part of the Kidd blood group system?

• Jka

• Jkb

• Jkc

• Jk3

Jkc

Why?

• The Kidd blood group system consists of three recognised antigens:

  • Jka → Major Kidd antigen

  • Jkb → Major Kidd antigen

  • Jk3 → High-prevalence antigen present on RBCs expressing Jka and/or Jkb

  • Jkc → Does not exist in the Kidd blood group system

• Clinical significance → Kidd antibodies (anti-Jka, anti-Jkb & anti-Jk3) can cause haemolytic transfusion reactions, particularly delayed haemolytic transfusion reactions (DHTRs)

Interpret the antibody screen results. What would you do next?

Interpretation: Positive antibody screen → possible anti-Fy^b or anti-P1

Why?

• The patient’s plasma reacts with screening cells 2 & 3, indicating the presence of an unexpected RBC antibody (or antibodies)

• Looking at the antigen composition sheet:

  • Fyb → Absent on cell 1, present on cells 2 & 3

  • P1 → Absent on cell 1, present on cells 2 & 3

• Both antigens match the reaction pattern. However, anti-Fy^b is a stronger initial suspicion because Duffy antibodies are predominantly IgG & react at the IAT phase

What would you do next?

1. Perform an 11-cell antibody identification panel to determine antibody specificity

2. Use additional testing if necessary, such as enzyme-treated cells (papain destroys Duffy antigens but enhances P1 reactions)

3. Confirm the identified antibody through patient phenotyping, where appropriate

4. If transfusion is required, select appropriate antigen-negative, crossmatch-compatible RBCs for clinically significant antibodies

For clinically significant antibodies: It is necessary to phenotype a patient’s red cells for an antigen that corresponds to the atypical antibody detected/identified in their plasma → TRUE or FALSE?

TRUE

Why?

• Phenotyping that patient’s red cells for the corresponding antigen demonstrates whether the patient is capable of forming the corresponding antibody. Phenotyping for multiple red cell antigens is also useful in complex investigations, in order to exclude the possibility of some antibodies (if the patient is suspected to have a mixture of atypical antibodies)

You can reliably phenotype a patient for red cell antigens if they have received a transfusion within the last 3 months → TRUE or FALSE

FALSE

Why?

• A patient who has received a red blood cell transfusion within the last 3 months cannot be reliably phenotyped using conventional serological methods

  • Donor RBCs → May still be circulating in the patient’s blood

  • Mixed-field reactions → Donor & patient RBCs may have different antigens, causing misleading results

  • Unreliable phenotyping → Results may reflect donor RBC antigens rather than the patient’s own antigens

  • Alternative → Molecular genotyping can determine the patient’s inherited RBC antigen profile

Part 1

You have performed a blood group and antibody screen on a patient.

The Patient’s blood group is A Rh(D) positive. The antibody screen results are shown in the image.

What is your interpretation of the antibody screen?

• Cold-reacting IgM antibody reacting with screening cells 1 and 3

• Warm-reacting IgM antibody reacting with screening cells 1 and 3

• Warm-reacting IgG antibody reacting with screening cells 1 and 3

• Warm-reacting IgG reacting with all screening cells

Warm-reacting IgG antibody reacting with screening cells 1 and 3

Why?

• The antibody screen is positive at the IAT phase, indicating a likely warm-reacting IgG alloantibody

  • RT & 37°C phases → No visible agglutination

  • IAT phase → SC1 & SC3 pos, consistent with IgG detected using AHG

  • Negative autocontrol → Supports an alloantibody rather than an autoantibody

  • Validation (yes) → Neg IAT reactions were successfully validated

Part 2

Here is the antigram for the screening cells:

What of the following statements is true?

• The results of the antibody screen match only with Anti-Jka, however, further testing is required to confirm

• The antibody may be Anti-e or Anti-Jka, further testing is required

• The antibody is Anti-Jka and we can identify this with matching the pattern of our results. No further testing required

• It is likely an antibody to an antigen of the Rh system, as the patient is Rh negative

The antibody is Anti-Jka and we can identify this with matching the pattern of our results. No further testing required

Why?

• From Part 1, the patient’s antibody screen showed:

  • SC1 = Pos (10)

  • SC2 = Neg (0)

  • SC3 = Pos (10)

• We compare this reaction pattern against the antigens expressed by each screening cell (see table layout)

• Both anti-e (Rh) & anti-Jk^a (Kidd) match the patient’s antibody screen

• However, we cannot determine which antibody is present using only these three screening cells

Part 3

You have performed phenotyping on this patient, and the results are as follows (assume controls produced expected results):

Which of the following statements is correct?

• The patient is capable of forming Anti-Jka

• The phenotyping results show the patient is Rh(D) negative

• The patient is capable of forming Anti-Jka because testing shows their red cells have the Jka antigen

• The patient likely has Anti-e, as their red cells agglutinated with Anti-e antisera

The patient is capable of forming Anti-Jka

Why?

• Jk^a absent → Patient can develop anti-Jk^a following exposure to Jk^a-pos RBCs

• e present → Patient would not normally produce anti-e because it is a self-antigen

• c & E absent → Patient could also develop anti-c or anti-E following sensitisation

Connection to Part 2

• Previously, the antibody screen suggested either anti-e or anti-Jk^a

• Phenotyping now helps distinguish them:

  • Anti-e → Unlikely because the patient expresses e

  • Anti-Jk^a → Possible because the patient lacks Jk^a

Therefore, anti-Jka is the leading suspected antibody, requiring confirmation with an antibody identification panel

Part 4

You have tested the patient’s plasma against antibody panels, and were able to identify and confirm the atypical antibody detected is Anti-Jka. This patient requires one unit of Packed Red Blood Cells (PRBCs). What further actions will you take?

• Grab a random unit of PRBCs from the fridge and assign it. No further testing required

• Select and phenotype for Jka negative PRBCs, IAT crossmatch

• Select and phenotype for Jka negative PRBCs, Immediate Spin Crossmatch

• Perform IAT crossmatch

Select and phenotype for Jka negative PRBCs, IAT crossmatch

Why?

• The patient has a confirmed anti-Jk^a antibody (Kidd system), which is clinically significant & can cause haemolytic transfusion reactions

  • Select Jka-neg PRBCs → Prevents the patient’s anti-Jk^a from reacting with donor RBCs

  • Phenotype donor RBCs → Confirms the selected units lack the Jk^a antigen

  • IAT crossmatch → Confirms serological compatibility between the patient’s plasma & donor RBCs at the antiglobulin phase

  • Immediate spin crossmatch → Insufficient because anti-Jk^a is predominantly IgG & may only be detectable at the IAT phase

Part 5

What are 2 other things you must consider when selecting compatible PRBCs for this patient?

• ABO Rh(D) compatible

• Whether another scientist has handled the PRBC recently

• PRBCs has not passed expiry date

• Whether the PRBCs is fresh (collected <5 days)

ABO Rh(D) compatible & PRBCs has not passed expiry date

You are setting up red cell phenotyping. You wish to use the screening cells for appropriate controls.

Here is the antigram of the screening cells:

Which cell would you select as a positive control for the E antigen?

• Cell 3

• Cell 1

• Cell 2

• None of these cells are suitable

None of these cells are suitable

Why?

• For selecting a positive control for red cell phenotyping, we must select a cell that has the weakest expression of the antigen we wish to type for. If applicable, we must select a cell that has HETEROZYGOUS expression of that antigen

• In this context, the cell we must use as a positive control for the E antigen must be E+e+. None of the screening cells in this antigram have that phenotype

Case study

A 65 yr old male with a history of MVA 5 years ago, for which he received 2 units of RBCs. He is scheduled for a cardiac bypass surgery. His blood bank test results are shown in the image

• 1) What is the patient’s blood group?

• 2) What is the interpretation of the antibody screen?

• 3) What needs to be done next?

1) The patient is AB Rh(D) pos because their RBCs express A, B & D antigens, while their plasma shows no reaction with A1, B or O reagent cells

2) Positive antibody screen, suggesting a warm-reacting IgG alloantibody

• Room temp (IS) → No recorded reactions

• 37°C → No recorded reactions

• IAT → Screening cell 2 shows a positive reaction (8), while cell 3 is negative (0)

• This suggests an unexpected antibody detectable at the IAT phase, consistent with IgG

• Comparing the antigen profiles, anti-E & anti-K are possible candidates, as both E & K are present on screening cell 2 but absent from cells 1 & 3

3) Perform an 11-cell antibody identification panel

The next steps are:

1. Verify & complete any missing screening results & controls

2. Perform an 11-cell antibody identification panel to identify the suspected antibody

3. Phenotype the patient’s RBCs to support antibody identification. His last transfusion was 5 years ago, so recent donor RBC interference is not expected

4. Select ABO/RhD-compatible, antigen-negative packed RBCs once the clinically significant antibody is identified

5. Perform an IAT crossmatch to confirm compatibility before surgery

Case study (con’d)

4) What antibody specificity would explain ALL reactions observed in both the antibody screen and antibody identification panel?

5) Are there any additional test that can be done?

6) What blood group should be given to the patient in case of transfusion?

4) Anti-K (Kell blood group system)

Why?

• The antibody identification panel shows positive reactions with cells 2, 8 & 9, all of which express the K antigen

• The antigen expression matches the reaction pattern as well

  • Anti-K → Predominantly IgG, detected at the IAT phase

  • Negative autocontrol → Supports an alloantibody rather than an autoantibody

  • Clinical significance → Anti-K can cause haemolytic transfusion reactions & HDFN

• The previous antibody screen also supports anti-K because only screening cell 2 expressed K & reacted

5) Phenotype the patient’s RBCs for the K antigen

• Test the patient’s RBCs using anti-K reagent

• Expected result → K-negative, supporting the identification of alloanti-K

• Confirm antibody specificity using the rule of three, which is already satisfied by the panel → three K-pos cells react & at least three K-neg cells do not

• Because the patient’s last RBC transfusion was five years ago, serological phenotyping should be reliable, assuming no other interference

6) AB Rh(D) pos, K-neg packed RBCs, with a compatible IAT crossmatch

• AB RhD pos → Matches the patient’s blood group

• K-neg → Prevents anti-K from reacting with donor RBCs

• IAT crossmatch → Confirms compatibility before transfusion

• Other ABO-compatible RBC groups may also be used if required, provided they are K-neg & crossmatch compatible

At the Australian Red Cross Blood Service (ARCBS) one donation of blood usually includes:

• 700-850 mls of blood

• 50-100 mls of blood

• 200-300 mls of blood

• 450-500 mls of blood

450-500 mls of blood

At the ARCBS blood is usually anticoagulated into:

• Citrate, phosphate, dextrose, adenosine (CPDA)

• Lithium heparin

• EDTA, phosphate and citrate (EPC)

• EDTA

Citrate, phosphate, dextrose, adenosine (CPDA)

Why?

• CPDA is an anticoagulant-preservative solution used in blood collection bags to prevent clotting & maintain RBC viability during storage

  • Citrate → Binds calcium (Ca2+), preventing blood coagulation

  • Phosphate → Maintains blood pH by acting as a buffer

  • Dextrose → Provides glucose for RBC metabolism & ATP production

  • Adenine → Supports ATP synthesis, maintaining RBC viability during storage

*Quiz says adenosine; however, the standard CPDA formulation contains adenine apparently

Viral screening of blood donor units includes testing for:

• Hepatitis B and C virus and antibody

• HTLV 1&2 antibodies

• HIV antibodies

• All of the above

All of the above

Why?

• Donated blood undergoes viral screening to prevent transmission of blood-borne infections to transfusion recipients

  • Hepatitis B (HBV) → Screening for viral antigens, antibodies & DNA

  • Hepatitis C (HCV) → Screening for antibodies & viral DNA

  • HIV → Screening for antibodies, antigen & viral DNA

  • HTLV-1 & HLTV-2 → Screening for antibodies

• These tests help identify infected donations & prevent potentially infectious blood from being transfused

All platelet donations were screened for bacterial contamination 24 minutes post collection → TRUE or FALSE?

FALSE

Why?

• All platelet donations screened for bacterial contamination 24 hours post collection

The ‘window period’ for the detection of the Hepatitis C virus (HCV) at the ARCBS (antibody & RNA testing) is approx.:

• 30 days

• 3 days

• 1 day

• 10 days

3 days

Why?

• The window period is the time between infection & when an infection can first be detected by a lab test

• Australian Red Cross Lifeblood uses HCV antibody testing & RNA testing (NAT) to screen donated blood

  • HCV antibody testing → Detects antibodies produced by the immune system, which take longer to develop

  • HCV RNA testing (NAT) → Detects viral genetic material much earlier

  • Combined testing → Reduces the estimated HCV detection window to approximately 3 days

Administration/transfusion of fresh frozen plasma (FFP) units to patients does not require a current group and hold (blood group with 72 hours/3 days validity for transfusion purposes) → TRUE or FALSE?

TRUE

Why?

• The transfusion of platelets and frozen products (FFP, cryoprecipitate) only require a historical blood group to be on the patient’s file to file for transfusion. The patient must have a valid group and hold (72 hour/3 day validity) for transfusion of PRBCs

Platelet concentrates:

• Are given to recipients to increase their clotting factors

• Need to be agitated while in storage

• Are usually stored in the fridge

• Have a shelf-life of approx. 2 weeks

Needed to be agitated while in storage

Why?

• Are stored at room temperature, shelf life of approx 5 days and given to increase platelet counts (not clotting factors)

Blood volume can be estimated as approx 50 mL/kg for adults, 100 mL/kg in children and 150 mL/kg in neonates → TRUE OR FALSE?

FALSE

Why?

• Blood volume can be estimated as approx 70 mL/kg for adults, 80 mL/kg in children and 100 mL/kg in neonates

Clinical features (signs & symptoms) of acute blood loss may include:

• Paleness

• Tachycardia

• Hypotension

• All of the above

All of the above

Why?

• Acute blood loss reduces circulating blood volume, causing hypovolaemia & reduced tissue perfusion

  • Paleness → Peripheral vasoconstriction reduces blood flow to the skin

  • Tachycardia → Heart rate increases to compensate for reduced circulating blood volume

  • Hypotension → Significant blood loss reduces venous return & cardiac output, causing decreased blood pressure

Chronic blood loss that has resulted in the patient developing iron deficiency anaemia (IDA) should be treated with blood transfusions (red cell concentrates) → TRUE or FALSE?

FALSE

Why?

• NEVER/RARELY transfuse in IDA; treat the underlying cause (blood loss) & oral iron therapy/intramuscular iron therapy

Case study 2

A 31-year-old female, G2P1 presents for her initial prenatal checkup

1) What is the patient’s blood group?

1) A Rh(D) pos

Why?

• Forward grouping: Anti-A pos & Anti-D neg → Group A

• Reverse grouping: A1 cells neg & B cells pos → Confirms group A

• RhD grouping: Anti-D pos → RhD pos

• Control → Neg, supporting valid RhD typing

Case study 2 (cont’d)

2) What is the interpretation of the antibody screen?

3) What needs to be done next?

2) Positive antibody screen - suspected warm-reacting IgG alloantibody

Why?

• The patient’s plasma reacts with screening cells 2 & 3, suggesting the presence of an unexpected RBC antibody

Which antibodies are suspected?

• According to the table layout, the reaction pattern is consistent with anti-c, anti-Fy^b or anti-Jk^a, but antibody specificity cannot yet be confirmed

3) Perform an 11-cell antibody identification panel

Case study 2 (still cont’d)

4) What antibody specificity would explain ALL reactions observed in both the antibody screen and antibody identification panel?

5) Are there any additional test that can be done?

4) Anti-Fy^b (Duffy blood group system)

Why?

• The reaction pattern matches anti-Fy^b

  • All Fy^b-pos cells react

  • All Fy^b-neg cells are non-reactive

  • The neg autocontrol supports an alloantibody

  • Anti-Fy^b is predominantly IgG & reacts at the IAT phase

• The previous antibody screen also supports anti-Fy^b because screening cells 2 & 3 were Fy^b-pos & reactive

5) Yes, patient phenotyping & enzyme testing

1. Patient phenotyping → Test the patient’s RBCs with anti-Fy^b. An Fy^b-neg result supports the identification of alloanti-Fy^b

2. Enzyme testing (papain) → Duffy antigens are destroyed by papain. Therefore, anti-Fy^b reactions should disappear when tested against papain-treated RBCs

3. Maternal antibody monitoring → Because the patient is pregnant, assess antibody levels & fetal risk according to antenatal protocols. Anti-Fy^b can occasionally cause HDFN

A baby was delivered by a mother who is AB Rh(D) negative.
The baby was jaundiced from birth. Upon examination of the baby’s blood film, there were many nucleated red cells and marked polychromasia. The baby’s blood group is A Rh(D) positive.

What is the most likely cause of the baby’s clinical features?

• HDFN due to Anti-D

• HDFN due to Anti-A

• Non-serological cause of jaundice

• HDFN due to Anti-Lea

HDFN due to Anti-D

Why?

• The mother is AB Rh(D) neg, while the baby is A Rh(D) pos. This RhD incompatibility can cause haemolytic disease of the fetus & newborn (HDFN)

  • RhD-neg mother → Lacks the D antigen & many produce anti-D following sensitisation

  • RhD-pos baby → Expresses D antigen inherited from the father

  • Maternal anti-D (IgG) → Crosses the placenta & binds fetal D-pos RBCs, causing extravascular haemolysis

  • Jaundice → RBC destruction increases unconjugated bilirubin

  • Nucleated RBCs & polychromasia → Indicate increased erythropoiesis as the baby compensates for haemolysis

Why not anti-A?

• The mother is blood group AB, so she does not normally produce anti-A or anti-B antibodies

A baby was delivered by a mother who is O Rh(D) negative.

The baby experienced increased jaundice after a few days. Upon examination of the baby’s blood film, there were some spherocytes. The baby’s blood group is A Rh(D) positive.

What is the most likely cause of the baby’s clinical features?

• HDFN due to Anti-A, but cannot fully exclude possibility of Anti-D also, due to blood group (at this stage)

• HDFN due to Anti-A

• HDFN due to Anti-D

• HDFN due to another Rh antibody

HDFN due to Anti-A, but cannot fully exclude possibility of Anti-D also, due to blood group (at this stage)

Why?

• Further testing such as DAT and elution are essential in determining which antibody is responsible for HDFN

Anti-Fya is an IgM antibody and can cause HDFN → TRUE or FALSE?

FALSE

Why?

• Anti-Fya is a warm-reacting IgG antibody, therefore is clinically significant (can cross the placenta)

Which test is useful in assessing the degree of foetal-maternal haemorrhage?

• Kleihauer test

• DCT

• Elution

• Antibody investigation

Kleihauer test

Why?

• The Kleihauer test detects & estimates the amount of fetal RBCs that have entered the maternal circulation, allowing assessment of fetomaternal haemorrhage (FMH)

  • Principle → Acid elution removes adult haemoglobin (HbA), while fetal haemoglobin (HbF) is resistant

  • Fetal RBCs → Retain haemoglobin & stain pink/red

  • Maternal RBCs → Lose haemoglobin & appear pale (ghost cells)

  • Clinical significance → Helps calculate the amount of anti-D immunoglobulin required for an RhD-neg mother following FMH

Why is Bilirubin, LDH and Haptoglobin part of a transfusion reaction investigation?

• To rule out haemolytic transfusion reaction

• To specifically identify ABO incompatible transfusion as the cause

• To assess TACO

• To monitor for infection

To rule out haemolytic transfusion reaction

Why?

• Bilirubin, LDH & haptoglobin are biochemical markers of haemolysis (RBC destruction). They help determine whether a transfusion has caused RBC destruction

  • Bilirubin↑: Increases as haemoglobin is broken down following RBC destruction

  • LDH↑: Released into the bloodstream when RBCs are damaged or destroyed

  • Haptoglobin↓: Binds free haemoglobin released from RBCs & is subsequently cleared from circulation

• These changes support a diagnosis of haemolytic transfusion reaction, although normal results alone do not completely exclude haemolysis

Anti-E is more commonly associated with what category of transfusion reaction?

• Delayed Haemolytic Transfusion Reaction

• Acute Transfusion Reaction

• Febrile Non-Haemolytic Transfusion Reaction

• TRALI

Delayed Haemolytic Transfusion Reaction

Why?

• Anti-E → Usually develops following exposure to E-pos RBCs through transfusion or pregnancy

• Antibody evanescence → Anti-E levels may decrease below detectable levels over time

• Anamnestic response → Re-exposure to E-pos RBCs triggers rapid antibody production

• Extravascular haemolysis → IgG-coated donor RBCs are predominantly destroyed by splenic macrophages

• Timing → DHTRs typically occur several days to weeks after transfusion

What is not part of a transfusion reaction investigation?

• Immediately disposing the suspected donor units in the bin

• Crossmatch on pre- and post- transfusion samples

• Clerical checks

• Visual inspection for haemolysis

Immediately disposing the suspected donor units in the bin

An ABO-incompatible transfusion is related to a

• Acute haemolytic transfusion reaction

• Delayed haemolytic transfusion reaction

• TACO

• TRALI

Acute haemolytic transfusion reaction

Why?

• An ABO-incompatible RBC transfusion can cause an acute haemolytic transfusion reaction because the recipient’s naturally occurring anti-A or anti-B antibodies (mainly IgM) attack incompatible donor RBCs

  • IgM binding → Recipient antibodies bind to A or B antigens on donor RBCs

  • Complement activation → IgM strongly activates the classical complement pathway

  • Intravascular haemolysis → Donor RBCs are rapidly destroyed within blood vessels

  • Clinical features → Fevers, chills, hypotension, back pain & haemoglobinuria

  • Timing → Usually occurs during transfusion or within 24 hrs

A Direct Antiglobulin Test (DAT) tests for:

• The presence of antibodies that have bound to red cells in vivo (inside the body)

• The presence of antibodies loose in plasma

• Antigens on the red blood cells

• The degree of foetal-maternal haemorrhage

The presence of antibodies that have bound to red cells in vivo (inside the body)

Why?

• The Direct Antiglobulin Test (DAT) detects IgG antibodies and/or complement (C3d) already attached to the patient’s RBCs in vivo

  • DAT → Detects RBCs sensitised with IgG or complement inside the body

  • AHG reagent → Binds to IgG and/or complement on RBCs, producing visible agglutination

  • Clinical significance → Used to investigate haemolytic transfusion reactions, HDFN & autoimmune haemolytic anaemia (AIHA)

Blood tests for a mother and baby were sent to the lab:

Mother: B Rh(D) positive, Anti-E detected

Baby: B Rh(D) positive, DAT positive

Check image for baby’s phenotype results

Which of the following statements is true?

• Mother’s Anti-E has crossed the placenta and bound to baby’s red cells, causing a positive DAT

• According to the baby’s phenotype results, the mother’s Anti-E is not the cause of the positive DAT

• Anti-E is not capable of crossing the placenta because it is an IgM antibody

• Mother’s Anti-D has crossed the placenta and bound to the baby’s red cells, causing a positive DAT

Mother’s Anti-E has crossed the placenta and bound to baby’s red cells, causing a positive DAT

Why?

• Mother has Anti-E. Anti-E is an IgG antibody and is capable of crossing the placenta

• Baby’s red cells do have the E antigen present. The Anti-E antibody is capable of crossing the placenta and binding to the E antigens on the baby’s red cells

• The antigen-antibody binding in vivo (inside the body) can be detected by a positive DAT

A patient has a normal PT and a prolonged APTT that corrects after a mixing study. Which finding is most consistent with this result?

• Factor VIII deficiency

• Factor VIII inhibitor

• Disseminated intravascular coagulation

• Severe liver disease

Factor VIII deficiency

Why?

• A normal PT, prolonged APTT, and correction after a mixing study indicate a deficiency of a factor in the intrinsic coagulation pathway

  • Normal PT → Extrinsic pathway is functionally normal

  • Prolonged APTT → Suggests a deficiency or inhibitor affecting the intrinsic pathway (factors VIII, IX, XI or XII)

  • Correction after mixing → Indicates a factor deficiency, because normal plasma supplies the missing clotting factor

  • Factor VIII deficiency → Causes prolonged APTT with normal PT, as seen in haemophilia A

Why not Factor VIII inhibitor?

• An inhibitor prevents normal clotting factor activity, so the APTT typically fails to correct or becomes prolonged again after incubation

In forward ABO grouping, the patient’s red cells are tested with:

• A1 and B reagent cells

• Anti-A and anti-B reagents

• Patient plasma and group O cells

• Anti-human globulin only

Anti-A and anti-B reagents

Why?

• Forward ABO grouping detects A & B antigens on the patient’s RBCs using commercially prepared antisera

  • Anti-A reagent → Detects A antigen on RBCs

  • Anti-B reagent → Detects B antigen on RBCs

  • Agglutination (+) → Corresponds antigen is present

  • No agglutination (0) → Corresponding antigen is absent

Why not A₁ and B reagent cells?

• A₁ and B reagent cells are used for reverse grouping to detect antibodies in the patient’s plasma

A patient’s red cells react with anti-A and anti-B. Their plasma does not react with either A1 or B reagent cells. What is the ABO group?

• A

• B

• AB

• O

AB

Why?

• The patient has both A & B antigens on their RBCs, but neither anti-A nor anti-B antibodies in their plasma

  • Anti-A (+) → A antigen present

  • Anti-B (+) → B antigen present

  • A1 reagent cells (0) → No anti-A detected

  • B reagent cells (0) → No anti-B detected

• Therefore, forward & reverse grouping confirm blood group AB

Why can group O red cells be incompatible with a patient with the Bombay phenotype A?

• Group O cells strongly express H antigen

• Group O cells strongly express A antigen

• Bombay patients have anti-DD

• Bombay patients lack ABO antibodies

Group O cells strongly express H antigen

Why?

• Individuals with the Bombay phenotype (Oh) lack H antigen on their RBCs & typically produce anti-H antibodies

  • Group O RBCs → Have high levels of H antigen because it is not converted into A or B antigens

  • Bombay phenotype → Lacks H antigen due to the hh genotype

  • Anti-H phenotype → Reacts with H antigen on normal group O RBCs, potentially causing severe haemolysis

  • Transfusion → Bombay patients generally require RBCs from another Bombay phenotype donor

Explain the difference between affinity and avidity in antigen-antibody interactions

• Affinity → Measures how strongly one antibody binding site attaches to a specific antigen epitope

• Avidity → Measures the combined strength of all antigen-antibody interactions, making the overall attachment stronger

• For example, IgM has high avidity because its pentameric structure allows multiple antigen-binding interactions

Why should heterozygous cells not always be used to rule out antibodies such as anti-Jk^a or anti-Fy^a?

Because anti-Jk^a & anti-Fy^a can demonstrate the dosage effect, meaning they react more strongly with homozygous RBCs than heterozygous RBCs

• Homozygous cells: Express more of the target antigen → Stronger reactions

• Heterozygous cells: Express fewer copies → Weaker or undetectable reactions

• Risk → A neg reaction with heterozygous cells may falsely rule out an antibody that is actually present

A patient is group A RhD positive, the current antibody screen is negative. The patient’s transfusion history shows that anti-K was detected 3 years ago.

Why donor red-cell unit is most appropriate, why?

A Rh(D) pos, K-neg donor RBCs with a compatible IAT crossmatch

Why?

• Although the patient’s current antibody screen is neg, they have a history of anti-K, a clinically significant IgG alloantibody

  • Antibody evanescence → Anti-K levels may decrease below detectable levels over time

  • Immunological memory → The immune system still remembers the K antigen

  • Anamnestic response → Re-exposure to K-pos RBCs can trigger rapid anti-K production

  • DHTR → This may cause a delayed haemolytic transfusion reaction

  • K-neg RBCs → Prevent re-exposure to the K antigen

  • IAT crossmatch → Confirms serological compatibility before transfusion

*A historically clinically significant antibody must always be considered, even when the current antibody screen is neg

Case study 3

A 65 yr old male with a history of MVA 5 years ago, for which he received 2 units of RBCs. He is scheduled for a cardiac bypass surgery. His blood bank test results are shown in the image.

1) What is the patient’s blood group?

1) A Rh(D) pos

Why?

• Forward grouping: Anti-A pos & Anti-B neg → Group A

• Reverse grouping: A1 cells neg & B cells pos → Confirms group A

• RhD grouping: Anti-D pos → RhD pos