Human Blood

Blood is composed of cells suspended in a liquid called plasma.

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Suspended in the plasma are three types of cells:
Red blood cells carry oxygen
White blood cells fight infection
Platelets stop bleeding in injuries
The most common type of grouping is the ABO (either uppercase or lowercase) grouping.

The varieties of glycoprotein coating on red blood cells divides blood into four groups:
A (A oligosaccharide is present)
B (B oligosaccharide is present)
AB (A and B oligosaccharides are present)
O (neither A nor B, only their precursor H oligosaccharide present)
There are subtypes under this grouping (listed as A1, A2, A1B or A2B…) some of which are quite rare. Apart from this there is a protein which plays an important part in the grouping of blood. This is called the Rh factor. If this is present, the particular blood type is called positive. If it is absent, it is called negative.
Thus we have the following broad categories:
A1 Negative (A1 −ve)
A1 Positive (A1 +ve)
A1B Negative (A1B −ve)
A1B Positive (A1B +ve)
A2 Negative (A2 −ve)
A2 Positive (A2 +ve)
A2B Negative (A2B −ve)
A2B Positive (A2B +ve)
B Negative (B −ve)
B Positive (B +ve)
B1 Positive (B1 +ve)
O Negative (O −ve)
O Positive (O+ve)