Learn: ABO Typing

Why is the ABO blood group system especially significant?

It is foundational to modern transfusion practice and is also relevant to organ and bone marrow transplantation.

"Who discovered the ABO blood group system and when?"

Karl Landsteiner in 1901.

"Which ABO groups were identified first by Landsteiner according to the lecture?"

"A, B, and O; AB was identified later."

What is Landsteiner's Law?

"Under normal circumstances, if a person has an ABO antigen on their RBCs, they should not have the corresponding antibody in their plasma."

Which ABO antibodies are discussed in the lecture?

"Anti-A, anti-B, and anti-A,B."

What are ABO isoagglutinins?

"Naturally occurring anti-A, anti-B, and anti-A,B antibodies."

What stimulates the development of naturally occurring ABO antibodies?

Immune exposure to environmental substances such as GI tract bacteria and pollen; transfusion exposure is not required.

At about what age do ABO isoagglutinins become noticeable?

Around 3-6 months of age; the lecture also notes that newborns do not have isoagglutinins until about 4 months.

Which immunoglobulin classes can ABO isoagglutinins include?

"IgM, IgG, and IgA; they are mostly IgM."

How can ABO isoagglutinins destroy RBCs?

They can fix complement and cause hemolysis.

At what temperature can ABO isoagglutinins agglutinate RBCs?

At room temperature.

Why can an ABO-incompatible transfusion be dangerous?

Naturally occurring antibodies can lyse and destroy RBCs that carry the corresponding antigen.

Which RBC groups can be destroyed by a person with anti-A?

A and AB RBCs.

Which RBC groups can be destroyed by a person with anti-B?

B and AB RBCs.

"Which RBC groups can be destroyed by a person with anti-AB?"

"A, B, and AB RBCs."

Where are ABO antigens found beyond red blood cells?

"The lecture lists WBCs, platelets, endothelium, epithelium, and secretions."

Name acute hemolytic transfusion reaction symptoms/signs listed in the lecture.

"Abdominal, chest, flank, or back pain; pain at infusion site; impending doom; hemoglobinemia; hemoglobinuria; hypotension; renal failure; shock; DIC; and death."

"What small volume of incompatible blood can cause an acute hemolytic transfusion reaction according to the lecture?"

As little as 10 mL.

What ABO antigens are listed for group A RBCs?

A and H.

What ABO antigens are listed for group B RBCs?

B and H.

What ABO antigens are listed for group AB RBCs?

"A, B, and H."

What ABO antigen is listed for group O RBCs?

H.

What antibodies are listed for group A plasma?

Anti-B.

What antibodies are listed for group B plasma?

Anti-A.

What antibodies are listed for group O plasma?

"Anti-A, anti-B, and anti-A,B."

What antibodies are listed for group AB plasma in the lecture table?

None are listed.

"Who produces anti-AB according to the lecture?"

Individuals with group O.

"What is a key feature of anti-AB?"

It reacts with A or B cells and can be IgG.

"Why is anti-AB clinically relevant in pregnancy?"

"It can cross the placenta and cause ABO hemolytic disease of the fetus and newborn (HDFN), which is typically not severe and may only require monitoring."

Which two gene systems interact to determine ABO/H expression in the lecture?

The H gene system and the ABO gene system.

On which chromosome is the H gene located?

Chromosome 19.

On which chromosome are ABO genes located?

Chromosome 9.

Which H allele is dominant and which is recessive?

H is dominant; h is recessive.

"How are A B and O described genetically in the lecture?"

A and B are dominant; O is recessive and described as an amorph.

How are genes passed from parents to offspring in the lecture's Mendelian model?

Each parent passes one allele of each gene pair to the offspring.

What are glycotransferases?

"Enzymes encoded by A, B, and H genes that modify precursor substances to produce the corresponding blood group antigen."

What is the genetic status of the O allele described in the lecture?

O is an amorph.

What does the H gene encode?

Alpha-2-L-fucosyltransferase.

"What sugar does the H transferase add and where?"

L-fucose is added to the terminal galactose of the precursor substance.

What H genotypes can produce H antigen?

HH or Hh.

What happens to H antigen production in hh individuals?

They do not produce H antigen.

What enzyme is encoded by the A gene?

Alpha-3-N-acetylgalactosaminyltransferase.

What sugar does the A transferase add to H antigen?

N-acetyl-D-galactosamine.

"Which ABO genotypes can produce A antigen assuming H antigen is present?"

"AA, AO, or AB."

Can A transferase attach A sugar to precursor substance in an hh individual?

"No; without H antigen, the A transferase will not attach to the precursor substance."

What enzyme is encoded by the B gene?

Alpha-3-D-galactosyltransferase.

What sugar does the B transferase add to H antigen?

D-galactose.

"Which ABO genotypes can produce B antigen assuming H antigen is present?"

"BB, BO, or AB."

Can B transferase attach B sugar to precursor substance in an hh individual?

"No; without H antigen, the B transferase will not attach to the precursor substance."

How do type 1 and type 2 precursor chains differ in linkage?

Type 1 has a beta 1-3 linkage between terminal galactose and N-acetylglucosamine; type 2 has a beta 1-4 linkage.

Where are type 1 precursor chains found?

In secretions and plasma.

Where are type 2 precursor chains found?

On red blood cells.

Is there a distinct "AB antigen"?

No. Group AB RBCs express both A and B antigens.

Is H antigen present in all common ABO blood types?

"Yes, in varying amounts; the Bombay phenotype lacks H antigen."

What is the order of H antigen amount on RBCs listed in the lecture?

O > A2 > B > A2B > A1 > A1B.

How does A2 compare with A1?

A2 is a weaker version of A1.

What is the Bombay phenotype also called in the lecture?

Oh.

What is the key antigen feature of the Bombay phenotype?

It lacks H antigen and therefore also lacks measurable A and B antigens.

Which naturally occurring antibodies can a Bombay individual possess?

"Anti-A, anti-B, anti-A,B, and anti-H."

Why is anti-H clinically important in Bombay individuals?

Anti-H can agglutinate RBCs that carry H antigen and can cause an acute hemolytic transfusion reaction.

Can a Bombay individual carry A or B genes despite lacking A/B antigen expression?

"Yes. They can have and pass on A and B genes, but without H antigen the transferases do not produce a measurable product."

What H genotype is always present in the Bombay phenotype?

hh.

What ABO alleles can a Bombay individual have?

"Any two of A, B, or O, according to the lecture."

What ABO blood types can a Bombay individual have children with?

"The lecture says Bombay individuals can have a child who is A, B, AB, or O."

Why might family studies or molecular testing be needed for a Bombay individual?

"To determine the underlying ABO blood type, which cannot be inferred from expressed A/B antigens alone."

How are ABO antigens expressed in newborns compared with adults?

A and B antigens are expressed more weakly in newborns.

Why should reverse ABO typing not be performed on newborns under 4 months old?

They have not yet developed their own ABO isoagglutinins; maternal antibodies may also be circulating or attached to the baby's RBCs.

How does weak newborn ABO antigen expression relate to ABO HDFN?

It is one reason ABO HDFN is generally less severe.

"Are the H and ABO genes inherited independently according to the lecture?"

Yes. The H gene and ABO gene are independent of each other.

A father is group B and a mother is group A. Can they have a group O child?

"Yes, if the father is BO and the mother is AO; each can pass an O allele, producing OO."

What ABO genotype(s) can produce group A phenotype?

"AA or AO, assuming functional H antigen expression."

What ABO genotype(s) can produce group B phenotype?

"BB or BO, assuming functional H antigen expression."

What ABO genotype produces group AB phenotype?

"AB, assuming functional H antigen expression."

What ABO genotype produces group O phenotype in the lecture?

"OO, assuming functional H antigen expression."

"What H genotypes are listed as possible for common A

B, AB, and O phenotypes?",HH or Hh.

What does forward ABO typing determine?

Which antigens are present on the patient's RBCs.

"In forward typing what does agglutination with a known reagent antibody mean?"

The patient's RBCs possess the corresponding antigen.

"In forward typing what does no agglutination with a known reagent antibody mean?"

The patient's RBCs do not possess the corresponding antigen.

Which reagent antibodies are routinely used for forward testing in the lecture?

"Monoclonal IgM anti-A, anti-B, and anti-D."

What is the expected forward reaction pattern for group A using anti-A and anti-B?

Anti-A positive; anti-B negative.

What is the expected forward reaction pattern for group B using anti-A and anti-B?

Anti-A negative; anti-B positive.

What is the expected forward reaction pattern for group AB using anti-A and anti-B?

Anti-A positive; anti-B positive.

What is the expected forward reaction pattern for group O using anti-A and anti-B?

Anti-A negative; anti-B negative.

What is the expected anti-H reaction for common ABO groups in the lecture table?

"A, B, AB, and O are positive, with amounts varying by type."

What is the expected anti-H reaction for Bombay (Oh) RBCs?

Negative.

What anti-D result is expected for D-positive and D-negative RBCs?

D-positive: positive with anti-D; D-negative: negative with anti-D.

"When is a control performed during forward typing and what should it show?"

When agglutination is observed in all forward reactions; the control should be negative.

What does a positive forward-typing control mean?

The blood type cannot be interpreted.

What controls can be used in forward typing?

Saline or the manufacturer's control.

What does reverse ABO typing determine?

Which antibodies are present in the patient's plasma.

"In reverse typing what does agglutination with reagent RBCs mean?"

The patient's plasma contains the corresponding antibody.

"In reverse typing what does no agglutination with reagent RBCs mean?"

The patient's plasma does not contain the corresponding antibody.

Which reagent cells are routinely used for reverse ABO typing?

A1 cells and B cells.

Is reverse typing performed for D (Rh) typing in the lecture's method?

No. There are no reverse reactions for D.

What is the expected reverse reaction pattern for group A plasma?

A1 cells negative; B cells positive.

What is the expected reverse reaction pattern for group B plasma?

A1 cells positive; B cells negative.

What is the expected reverse reaction pattern for group AB plasma?

A1 cells negative; B cells negative.

What is the expected reverse reaction pattern for group O plasma?

A1 cells positive; B cells positive.

What is the expected reverse reaction pattern for Bombay (Oh) plasma in the lecture table?

"A1 cells positive, B cells positive, and O cells positive."

What is required for a valid ABO interpretation?

"Forward and reverse reactions must match/be complementary, except reverse testing is not performed in neonates under 4 months."