Blood Group

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.

Also Known As:  Blood Group, Rh Factor, ABO Grouping, Blood Typing, ABO Group

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.

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).

Sample

• 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.

Indications

1. ABO blood grouping and Rh typing are done.
2. Blood grouping is done for the donor and the recipient (Crossmatch).
3. Blood grouping is done in the expected mother and newborn.

Table showing antigen and antibody:

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