Blood Grouping

DR. RAFIQ AHMAD

ABO & Rh(D) Blood Groups

The ABO System

Discovered in 1901 by Dr. Karl Landsteiner

4 Main Phenotypes (O, A, B, AB,) ABO gene located on long arm of

chromosome 9

- ABO, Hh, Sese

The ABO Antigens

Added to Proteins or Lipids in Red Cells Substrate Molecule is H (fucose) A antigen is N-acetyl-galactosamine (GalNAc) B antigen is Galactose (Gal) A and B genes code for transferase enzymes

Blood group (or blood type)

ABO group Biochemistry

ABO Sub groups

ABO Antibodies Antibodies produced to “non-self” Produced after first few months of life A & B people have mainly IgM O people have IgG May fade in old age

A: A1, A2, A3, Ax, Am, Ael …, A(B)B: B3, Bx, Bm…, B(A)

Inheritance of ABO Groups

Allele from the mother

Allele from the father

Genotype ofoffspring

Blood types ofoffspring

A A AA A

A B AB AB

A O AO A

B A AB AB

B B BB B

B O BO B

O O OO O

Distribution of ABO Groups

PopulationO A B AB

Aborigines 61 39 0 0 Basques 51 44 4 1 Blackfoot (N. Am. Indian) 17 82 0 1 Saudies (Eastern Province) 49 27 19 5 Chinese-Canton 46 23 25 6 Chinese-Peking 29 27 32 13 English 47 42 8 3 Hawaiians 37 61 2 1 Irish 52 35 10 3 Mayas 98 1 1 1 Navajo (N. Am. Indian) 73 27 0 0 Peru (Indians) 100 0 0 0 United Kingdom (GB) 47 42 8 3 USA (blacks) 49 27 20 4 USA (whites) 45 40 11 4

Distribution of the A allele

Distribution of the B Allele

Distribution of the O Allele

ABO Typing

Cell Group Test Washed Cells With: Monoclonal Anti-A Monoclonal Anti-B Inert control

Agglutination is a positive result

Reverse Group Test plasma/serum with: Known A1 cells Known B cells Known O cells ? Known A2 cells

Reactions may be weaker than cell group

Significance of ABO Group

ABO mismatched transfusions: Rare May be life threatening Can be caused by technical or clerical error Intravascular haemolysis More severe in group O patients

Universal Donor and Recipient

Universal Donor Group O

Carries no A or B antigens

Packed and processed units have little antibody

Universal Recipient Group AB

Patient has no anti-A or anti-B present

Cannot lyse any transfused cells

Beware: other

antibodies may be present

Patient’s own group should always be preferred

The Rh(D) Antigen

Rh is the most complex system, with over 56 antigens

Discovered in 1940 after work on Rhesus monkeys

Subsequently discovered to be unrelated to monkeys

Rh gene located on short arm of chromosome 1

In mid 1940’s other Rh antigens C, c, E, and e were discovered

Simple Genetics of Rh(D)

97% of asians are Rh(D) pos The antithetical antigen d has not been found The d gene is recessive:

Dd, dD, DD, persons are Rh(D) pos Only dd persons are Rh(D) neg

Distribution of Rh(D) Types

Population Rh(D) pos Rh(D) neg

Caucasian(Saudis), E Pro.

86%(90.5)

14%(9.5)

African-American 95% 5%

Oriental >99% <1%

Significance of Rh(D)

80% of Rh(D) neg persons exposed to Rh(D) pos blood will develop anti-D

Anti-D can also be stimulated by pregnancy with an Rh(D) positive baby Sensitisation can be prevented by the use of anti-D

immunoglobulin, antenatally and post natally

Rh(D) neg females of childbearing potential should never be given Rh(D) positive blood products

Inheritance

ABO & Rh genes are not linked ABO & Rh(D) type are inherited independently

For example:An A Rh(D) pos mother

and a B Rh(D) pos father

could have an O Rh(D) neg child

Rh Typing

Routine Rh typing

for donors and

patients involves

typing for only the

D antigen.

D Testing

Routine D antigen testing involves testing the patient RBCs with anti-D commercial antisera

If the D antigen is present, it should agglutinate strongly with anti-D at Immediate Spin (IS) If you’re Rh+, you have the D antigen If you’re Rh-, you do not have the D antigen

Weak D phenotype

Some D-positive RBCs DO NOT react at Immediate Spin using commercial anti-D

In these cases, AHG testing is needed to determine the D status

Weak D testing

If negative at IS, patient cells and anti-D reagent are incubated at 37° for 20 minutes, then centrifuge

If still negative, wash x3 and add AHG If negative, add CC and report as Rh negative (if CC

agglutinate) If positive, report as Weak D Positive

Patients who require AHG testing to determine the presence of the D

antigen are called “Weak D Positive”

Weak D (Du) Phenotype

Weak D can be inherited in three ways: Incomplete/Partial antigen (D mosaic) Due to the position effect Weakened expression of D

Partial D (D Mosaic)

Missing one or more parts of the D antigen Since the antisera is specific for the whole D

antigen, a weak reaction may result if patient has a partial antigen

Why is Partial D is significant? If the patient is transfused with D positive red

cells, they may develop an anti-D alloantibody* to the part of the antigen (epitope) that is missing

* alloantibody- antibody produced with specificity other than self

Position Effect

Gene interaction effect C allele is in trans position to D allele Does not occur when C is in cis position Steric hindrance causes the anti-D reagent to

weakly attach (C antigen crowds the D antigen)

Inheritance of ABO and Rh(D)

Mother

Group A AO

Rh(D) pos Dd

Father

Group B BO

Rh(D) pos Dd

Group A AO

Rh(D) pos Dd

Group B BO

Rh(D) pos Dd

Group O OO

Rh(D) neg dd

AABB Standards

Require weak D testing on all donor red blood cells that do not agglutinate at IS

DO NOT require weak D testing on recipient blood each facility has their own protocol If only IS is performed and patient is negative, they will

receive negative units However, some labs don’t like to waste D-negative units, so

they take the test to AHG If the patient is positive, they may receive D-positive units

(it would be rare that the patient is a Partial D)

The end!!

Thank you