ABO Blood Group System

Blood Groups 

• Inherited character of the red cell surface. detected by a specific antibody . 
• Most blood groups are organized into blood group systems. 
• Most blood group antigens are protein or glycoprotein. 
• Some blood group antigens are carbohydrate structures on proteins or lipids. 
• The two most important blood group systems from the clinical point of view are ABO and Rh. 

Discovery of ABO Groups (1901) 

• Inheritance of ABO Blood Groups 
• Three allelic genes -A, B & O 
• Follows Mendelian principles 
• A and B genes co-dominant 
• O gene is amorphic 
• ABO gene on chromosome 9q34 
• Discovered by Yamamoto in 1990 

Structure of the Red Cell Membrane

• Development of ABO 
• Antigens & Antibodies 
• Antigens - 6th week of fetal life 
• Full expression -3 years after birth 
• Glycoproteins, 
• Can be Glycolipids or Glycosphingolipids 
• Present on most tissues 
• RBC, endothelial cells, platelets, lymphocytes, epithelial cells. 
• Soluble form in secretions 
• Saliva, tears, urine, bile, milk, digestive juice, amniotic fluid 
• Antibodies- after first few months of life 
• Too low for detection until 3- 6 months of age 
• Antibody levels- peak at 5 to 10 years of age 
• Immunoglobulin class – usually IgM and few IgG 
• Activate compliments 
• Naturally occurring antibodies 

Bombay Phenotype

• First reported by Bhende, Bhatia et al in Bombay in 1952 
• Red cells lack A, B and H antigens 
• Serum has anti-A, anti-B and anti-H antibodies 
• Red cells show no reaction with anti-H 
• Frequency of this group in Bombay estimated to be about 1 in 7600 while in South West districts of Maharashtra about 1 in 4500 

Clinical significance 

• Cause immediate intravascular red cell destruction 
• Which can give rise to severe and fatal HTR. 

The ABO Blood Group System

Blood Grouping

1. Cell grouping-

• To detect the presence or absence of A and B antigens on red cells.
• Test RBCs with Standard monoclonal antisera

   2.Serum grouping-

• To detect the presence or absence of Anti A and Anti B naturally occurring antibodies in the serum.
• Test serum with known cells
• Discrepancy if cell and serum grouping do not agree
• Conventional tube method
• Results in Tube method
• Reading in tube method

Matching blood groups for Transfusion

• Rh and other important Blood Group Systems
• The most complex blood group system and second most important blood group system.
• More than 50 Rh related antigens.
• Rh D is the most important antigen, Other important antigens are C, E,c and e.
• —Non glycosylated proteins.
• —Rh antibodies - immune antibodies
• ( IgG, 370C reactive, Do not bind compliments)
• — Clinical significance- dhtr and HDN

Direct Antiglobulin Test

• Detect in vivo sensitization of red cells with IgG and / or C3d
• Perform DAT using polyspecific AHG reagent.
• EDTA sample should be used for DAT testing

Antibody Screening

• SSerum is tested against a panel of single donor group O red cells
• SPanel should express antigens considered clinically relevant in the population
• SAn antibody is considered to be clinically significant if examples with that specificity are known to have caused HDN, NTR or unacceptably short survival of red cells
• SAntibodies reactive at 37oC and/or in IAT are more likely to be clinically significant
• SShould also have cells with homozygous expression of antigens that are dangerous and show dosage – Jka, Jkb, Fya, Fyb, K

Interpretation

• Negative Antibody Screen
• SProvides a high degree of confidence that the patient’s plasma is free of unexpected antibodies
• Positive Antibody Screen
• SIndicates the presence of a red cell antibody
• SAn antibody investigation is necessary to identify the specificity of the antibody
• SThe antibody screen does not identify the antibody
• Compatibility Test
• Donor red cells are tested with recipient plasma to detect ABO antibodies in the recipient plasma that will agglutinate or sensitise the infused donor red cells
• 1.Albumin/Saline Method
• drops serum, 2 drops albumin, I drop cell 45 mins
• LISS additive Method
• 2 drops serum, 1 drop cells, 2 drops LISS additive, 10 mins
• Spun and read after incubation - IgM direct agglutination
• AHG added - spun and read - IgG sensitisation