Blood Types

There are many who do not understand blood types. A person’s blood type is determined by the presence or absence of certain alleles (proteins) on the surface of their blood cells. Many of these alleles are what are called antigens, in that they will prompt an immune system antibody response. Sometimes these responses can have fatal consequences.
For blood transfusion compatibility, there are three antigens of primary concern. These are:
A
B
D (called “the RH factor”, since it was the first allele common to humans and the Rhesus monkey found)
If you receive a transfusion of blood containing one of these that you do NOT already have, your immune system response will cause clotting, and death.
In a nutshell, if you have A, you are A type. If you have B you are B type. If you have both, you are AB type. If you have neither, you are O (Other) type. Whether or not you have D is shown by a + (you have it) or a – (you do not have it).
From a transfusion compatibility standpoint, the following is pretty much it.
If you are X: you can take Y
O+: O-, O+
O-: O-
A+: O+, O-, A+, A-
A-: O-, A-
B+: O+, O-, B+, B-
B-: B-, O-
AB+: O+, O-, A+, A-, B+, B-, AB+, AB-
AB-: O-, A-, B-, AB-
Notice that any of them can take O-, which is called the “universal donor”. Note that AB+ can take any of them, and is called the “Universal Recipient”.
There are other “types” as well. There is one called RH Null. There are a very few people have none of the 61 alleles in the RH Group (all alleles common to humans and the Rhesus Monkey). These people are called RH Null, and can only take other RH Null blood as the normally less than fatal reactions to each of the rest of the RH Group of antigens add up to being fatal when the are ALL absent. At last count, there were less than 50 such people alive.
There are around 300 different alleles on the surface of blood, but introduction of them does NOT induce a life threatening blood clotting situation except when a large number of them are mismatched.
A very rare type is CIS AB. This may be RH- or RH+ as in AB- or AB+ blood. It is different in that one antigen produces both the A antibody and the B antibody. This is truly a “fusion” hybrid. From a transfusion compatibility standpoint, it is no different than “normal” AB types.