Chapter 5: ABO Blood Group System

Why is the ABO system the most clinically significant blood group system?

ABO antibodies are naturally occurring and can cause fatal hemolysis

What type of hemolysis can ABO incompatibility cause?

immediate intravascular hemolysis

Why is ABO compatibility essential in transfusion and organ transplant?

To prevent immune destruction of donor cells

What antigen is found on type O red cells?

H antigen only

What does the O gene code for?

Nothing; it's amorphic (non-functional)

why is the O antigen considered amorphic?

no detectable antigen is produced in response to the inheritance of the O gene

What effect does the O gene have on the H antigen?

Leaves it unmodified (no A or B antigen made)

Genotype possibilities for type A?

AA or AO

Genotype possibilities for type B?

BB or BO

Genotype for type AB?

AB

Genotype for type O?

OO

If a child is type O, what must both parents carry?

An O gene

If a child is AB, what must each parent contribute?

One A gene and one B gene (e.g., A + B parents)

where are ABO genes located and what do they do?

located on chromosome 9 and encode enzymes that synthesize the A and B antigens on RBCs

where are Hh genes located and what do they do?

located on chromosome 19 and are closely linked to Hh genes.

Encode another fucosyltransferase that produces the H antigen in bodily secretions

What does the Hh gene do?

produces H antigen required for expression of A and/or B

What happens if someone has hh genotype?

No H antigen → Bombay phenotype

What does the Se gene control?

Secretion of A, B, and H substances in body fluids

Enzyme from H gene?

L-fucosyltransferase

Enzyme from A gene?

N-acetylgalactosaminyltransferase

Enzyme from B gene?

D-galactosyltransferase

Enzyme from O gene?

none

sese h genotype → enzyme activity?

None; no H antigen, no secretions

Sugar added by L-fucosyltransferase?

L-fucose

Sugar added by N-acetylgalactosaminyltransferase?

N-acetyl-D-galactosamine

Sugar added by D-galactosyltransferase?

D-galactose

where are ABO antigens found?

on RBC membranes

Where are ABO substances found?

in secretions (if Se gene is present)

What gene is required for H antigen?

H gene (dominant allele)

What modifies H antigen into A or B antigens?

A or B genes

What gene allows A/B/H in secretions?

Se gene

What does forward typing detect?

RBC antigens

What does reverse typing detect?

Serum antibodies

Sese or SeSe genotype: What's in secretions?

A, B, and/or H substances

sese genotype: What's in secretions?

nothing

Bombay genotype?

hh

Forward/reverse typing in Bombay?

Types as O; reacts with all O cells (anti-H)

Auto control in Bombay?

negative

Ulex europaeus result in Bombay?

negative (no H antigen)

What blood can Bombay individuals receive?

Bombay blood only

Which group has the most H antigen?

O

Which group has the least H antigen?

A1B

General order of H antigen amounts?

O > A2 > B > A2B > A1 > A1

What is chimerism?

presence of two genetically distinct cell populations

What causes chimerism?

transfusion, twin blood sharing, bone marrow transplant

What is cis-AB?

Both A and B genes on one chromosome

What does cis-AB phenotype look like?

Weak expression of A and B antigens

Most common blood type in whites?

O (45%)

Most common blood type in Blacks?

O (49-50%)

Least common ABO type in all groups?

AB (4%)

Why are ABO antibodies "expected"?

stimulated by environmental antigens (bacteria, pollen)

Why skip reverse typing in newborns?

ABO antibodies not yet developed (start ~4-6 months)

Forward grouping reagents?

Anti-A, Anti-B, Anti-A,B (Anti-H if needed)

Reverse grouping reagents?

A1 cells, B cells

What does Anti-A,B detect?

Both A and B antigens

Why use Anti-A,B?

Confirm group O or resolve discrepancies

What is an ABO discrepancy?

forward and reverse typing results don't match

Expected ABO reaction strength?

3+ to 4+

What can cause weak reactions?

Subgroups, disease, transfusion, age

What is Wharton's jelly?

cord substance causing false positives in newborn typing

How to fix Wharton's jelly issue?

Wash cord cells 3-7 times

What percent of A people are A2?

~20%

What does A2 phenotype lack?

Reactivity with anti-A1 lectin

What can A2 individuals form?

Anti-A1

What is mixed field agglutination?

Some cells agglutinate, some don't (dual population)

What causes mixed field agglutination?

Recent transfusion, A3 subgroup, chimerism

ISBT number for ABO system?

001

What is ISBT used for?

standardized naming of blood groups globally

Universal RBC donor?

O negative

Universal plasma donor?

AB plasma

Who can type A receive RBCs from?

A or O

Who can type AB receive RBCs from?

A, B, AB, or O (universal RBC recipient)

Who can type O receive plasma from?

O, A, B, AB (universal plasma recipient)

Why is AB plasma safe for everyone?

No anti-A or anti-B antibodies