Blood bank study guide

What is the definition of a "clinically significant" antibody

Antibodies that cause decreased survival of RBCs. Typically IgG reacting at 37°C or in the AHG phase of IAT

What is the definition of an Autoantibody and why are they clinically significant?

Antibodies produced against antigens expressed on one’s own RBCs. May complicate the detection of clinically significant antibodies

Why do you include a 37-degree incubation phase and antiglobulin in the antibody screen?

• Mimics human body temp which is optimal for IgG antibodies to bind.

• AHG, when added, can cause visible agglutination if patient has antibodies

Reagent red cells used for screening cells and antibody panels are group O, why?

So that naturally occurring Anti-A or anti-B will not interfere with detection of unexpected antibodies

Explain the difference between a homozygous and a heterozygous antigen expression on a cell

Homozygous antigen expression shows dosage and is stronger than heterozygous antigen expression which is weaker in terms of dosage

Why are enhancement reagents used in the antibody screen

To increase the sensitivity of the test system

What is the purpose of Anti Human Globulin (AHG) in an antibody screen?

To detect clinically significant non ABO IgG antibodies and complement bound to RBCs

What is the purpose of Coombs Check Cells in the antibody screen

To validate the results of negative IAT/DAT in an Antibody screen

What questions can you ask to help yourself interpret an antibody screen?

• In what phases did the reaction(s) occur

• Is the autologous control -/+

• Did more than 1 screen cell sample react

• Is hemolysis or mf agglutination present

• Are the cells truly agglutinated or is rouleax present

What are the limitations to the antibody screen?

• Antibody titer below the level of sensitivity

• Low-prevalence antibody and antigens

• Lack of homozygous expression of the target antigen on screening cells

How does the patient history play a role in the antibody identification?

Provides clues to verify complex reaction patterns, ensures the selection of safe antigen negative blood for transfusion

When interpreting panel results, what considerations should be made?

• Rule out false +’s

• Identify clinically significant alloantibodies

• Evaluate reaction strengths

Explain the principles behind enzyme and neutralization techniques

• Enzymes act as biological amplifiers

• Neutralization techniques mask interfering substances

Explain Adsorption techniques used in conjunction with panels for antibody ID.

Removes specific Antibodies from patient serum/plasma by binding them to RBCs

What is an antibody to a high frequency antigen?

Anti-K

What is an antibody to a low frequency antigen?

Anti-Kpa

List the characteristics of Lewis antigens and antibodies.

• On type 1 glycophingolipids that are absorbed onto RBCs

• LEa & LEb are primary concern antigens

• Antibodies are generally IgM & do not cross the placenta

• Anti-Lea most common

• Le antibody can be neutralized with Le antigen+plasma

• Most often react at RT but can also be detected at 37°C

Explain the changes of Lewis antibodies in pregnant women.

• Neutralize with Le antigen when testing for HDN antibodies

• Phenotype shift to Le(a-b-)

• starts producing naturally occurring Anti Le-a or anti-Le-b antibodies

Differentiate between Lea and Leb antibodies.

• Lea is more stronger and more common than Leb which is weaker and more rare

What is the clinical significance of Lewis antibodies?

Not clinically significant, inactive at 37°C and don’t cross the placenta (IgM)

Define a blood group system

classifies blood based on inherited antigens on RBCs

List MNSs group characteristics

• Located on glycophorin A (GPA)

• Antigens are easily destroyed by enzymes

• M antibodies cause ABO discrepancies

• M & N antibodies don’t cause HDN and HTR, are IgM

• S & s antibodies cause HDN and HTR, are IgG

• M & N antibodies react at RT

• S & s antibodies react at 37°C

List P group characteristics

• IgM, naturally occurring in P1 individuals

• Cold reacting Antibody (4°C)

• HTR & HDFN not associated with P1

• has two common phenotypes; P1 & P2

List I group characteristics.

• Infant RBCs are high in i antigens until 18 months when they develop I antigen on RBCs

• Anti-I is a common autoantibody, not associated with HDFN or HTR

• Cord blood cells lack I and carry i

• Auto-anti i reacts at 4°C, associated with infectious mono

• Pathogenic auto-anti I is associated with hemolytic anemia

List Kell group characteristics

• K is rated second in immunogenicity, most common in Blood bank & is strongly immunogenic

• Most Anti-K appear to be induced by pregnancy and transfusion

• Anti-k—low prevalence antigen—<10%

• k antigen has a high prevalence antigen—98%

• IgG antibodies that do not react at room temp

• Can be heterozygous

List Duffy group characteristics.

• IgG antibody

• React at 37°C & AHG

• Anti-Fya more common than anti-Fyb

• Destroyed by enzymes

• Cause HTR & HDN

• Demonstrate dosage

List Kidd group characteristics

• IgG antibody

• Cause delayed HTR

• React at 37°C & AHG

• Often weak dosage

• Enhanced by enzymes

List Lutheran group characteristics.

• Anti-Lua has low prevalence, IgM—not clinically significant

• Anti-Lub has high prevalence, IgG, associated with HTR & HDN

  • is rare

What are the rules for antibody identification on a panel?

• Test patient serum (unknown) with reagent RBCs (known)

• Rule of 3

• Landsteiner’s Rule

• Add check cells to any negative AHG

• Look for a matching pattern

• Rule out negative cells

• Is autologous ±

• Circle antigens that are not crossed out

What is dosage and how does it affect reactions on a panel

• Dosage is multiple antibodies. Can be strong if homozygous panel cells or weak if heterozygous panel cells (exclusing K)

Calculate the number of units required to be tested when a patient has an Anti-E and a Anti-K , E frequency = 30%, K frequency = 9%; you need 4 compatible units to crossmatch.

7 units

Which of the major antibody groups are enhanced or destroyed by enzymes

• Destroyed: M, N, S, s, Duffy

• Enhanced: Rh, Kidd, Lewis, I, P

Why do you need to antigen type a Patient or unit after completing a panel ID

• To ID the alloantibody

• To confirm that they lack the corresponding antigen for the identified antibody

Why is an Auto-control run when you are doing an antibody screen or panel

• If negative=alloantibody

• If positive=autoantibody

State the principle of the antiglobulin test.

• RBCs coated in vivo with IgG and/or complement

• Applications in: HDN, HTR, and AIHA

• Sample should be collected in an anticoagulant such as EDTA

Differentiate between monospecific and polyspecific AHG (coombs).

• Monospecific AHG is Anti-IgG and Anti-complement

• Polyspecific AHG has specificities

Differentiate between the Indirect Antiglobulin Test (IAT), and the Direct Antiglobulin Test (DAT).

• IAT has a two stage procedure

• DAT has a one-stage procedure

What clinical conditions can result in a positive DAT

antibodies or complement proteins coat the surface of your red blood cells in vivo

Name 2 procedures which can be used to identify an antibody in a Positive DAT situation.

• Elution

• Adsorption

What are 2 ways a DAT may be detected

• Tube method

• Gel card method

List the characteristics of Cold Reactive Autoantibodies

• React at RT with most (if not all) of the panel cells and give a positive autocontrol

• DAT is usually positive with anti-C3 AHG (detects complement)

• Could be due to infectious mono, CAD, or Mycoplasma pneumoniae

List the characteristics of a Warm Reactive Autoantibody?

• More common than cold autoantibodies

• Positive DAT due to IgG antibodies coating the red cell

• The majority of panel or screening cells will be positive

• Cause warm autoimmune hemolytic anemia

• The Rh system (e antigen) seems to be the main target

Why does an individual normally not produce antibodies against antigens that are present on their own red blood cells?

Their immune system recognizes these antigens as self and does not attack them.