There are four main blood groups (types of blood) – A, B, AB and O. Your blood group is determined by the genes you inherit from your parents.
Each group can be either RhD positive or RhD negative, which means in total there are eight main blood groups.
Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma. Your blood group is identified by antibodies and antigens in the blood.
Antibodies are proteins found in plasma. They are part of your body’s natural defenses. They recognize foreign substances, such as germs, and alert their immune system, which destroys them.
Antigens are protein molecules that are found on the surface of red blood cells.
ABO grouping can be performed in two ways
Forward grouping/Cell grouping: Red blood cells are tested for A and B antigens using known anti-A and anti-B sera.
Reverse grouping/Serum grouping: Serum is tested for anti-A and anti-B anibodies using known A and B red cells.
The ABO system
There are four main blood groups defined by the ABO system:
- blood group A – has A antigens on the red blood cells with anti-B antibodies in the plasma
- blood group B – has B antigens with anti-A antibodies in the plasma
- blood group O – has no antigens, but both anti-A and anti-B antibodies in the plasma
- blood group AB – has both A and B antigens, but no antibodies
Blood group O is the most common blood group. Almost half of the population (48%) has blood group O.
The Rh system
Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it’s absent, your blood group is RhD negative.
This means you can be one of eight blood groups:
- A positive (A+)
- A negative (A-)
- B positive (B+)
- B negative (B-)
- O positive (O+)
- O negative (O-)
- AB positive (AB+)
- AB negative (AB-)
About 85% of the population is Rh positive (36% of the population has O+, the most common type).
- This can be done on whole blood or even on clotted blood.
- The sample can be stored at 4 °C. and stable for 5 days.
- Some time week subgroup may result in mistyping where Coombs test may be helpful.
- ABO blood grouping and Rh typing are done.
- Blood grouping is done for the donor and the recipient (Crossmatch).
- Blood grouping is done in the expected mother and newborn.
Blood grouping reagents
The blood Grouping reagents enables rapid identification of ABO blood group and Rh factor depending upon the antigen present on the surface of red blood cells.
Blood Grouping reagent
|Anti A Sera||Blue||5 ml||2-8 °C|
|Anti B Sera||Yellow||5 ml||2-8 °C|
|anti-D||Clear||5 ml||2-8 °C|
Blood grouping Procedure
- Inform the patient or individual about the procedure to be carry out
- Dangle the hand down to increase the flow of blood in the fingers.
- Clean the fingertip to be pierced with spirit or 70% alcohol (usually ring or middle finger) and gently massage the finger to increase blood flow
- With the help of the sterile lancet or pricker, pierce the fingertip and place one drop of blood in each of the four cavities
- Now add one drop of each antiserum into each cavity respectively
ABO and Rhesus Blood Grouping Tiles
- Mix each blood drop with the antiserum using a fresh mixing stick or applicator stick
- Now you can observe agglutination in the form of fine red granules within 30 seconds. Anti RhD takes slightly longer time to agglutinate compared to Anti A and Anti B.
Blood Grouping Result and Interpretation
|Slide Number||Anti A||Anti B||Anti RhD||Blood Group|
|Slide 1||✓||X||✓||A +ve|
|Slide 2||X||✓||✓||B +ve|
|Slide 3||✓||✓||✓||AB +ve|
|Slide 4||X||X||✓||O +ve|
- ✓: Agglutination
- X : No agglutination
Blood grouping result interpretation
- If agglutination is observed when individual’s blood is mixed with Anti A reagent, then the individual is said to have a blood group “A”.
- If agglutination is observed when individual’s blood is mixed with Anti B reagent, then the individual is said to have a blood group “B”
- If agglutination is observed when individual’s blood is mixed with Anti A and Anti B reagent, then the individual is said to have a blood group “AB”
- If no agglutination is observed when individual’s blood is mixed with Anti A and Anti B reagent, then the individual is said to have a blood group “O”
- If agglutination is observed when individual’s blood is mixed with Anti RhD reagent, then the individual is said to have a “+ve” Rh factor.
- If no agglutination is observed when individual’s blood is mixed with Anti RhD reagent, then the individual is said to a have “-ve” Rh factor.
Common setback during Blood grouping
|False positive result||Occurs when the antisera reagents mix with each otherOccurs when Incubated for a longer time||Being ensuring that the antisera reagents are added properly onto the respective cavity without spilling to the sides The results should be read within the time period mentioned in the manufacturer’s guide|
|No agglutination observed||Mostly occurs when the antisera are not stored under proper conditions||Always ensure that the antisera are stored in refrigerator (2-8oC)|
Possible References Used