There are four basic blood types.
  • A
  • B
  • AB
  • O
And their basic relationships are as follows:
  1. Donating

    • Type A can donate to A or AB
    • Type B can donate to B or AB
    • Type AB can donate to AB only
    • Type O can donate to anyone
  2. Receiving
    • A can receive from A or O
    • B can receive from B or O
    • Type AB can receive from anyone
    • O can only receive from O

There is also an Rh factor attached to a blood type which is the + or -. The plus means there is protein present in your blood. A minus denotes a lack of protein. A person with a negative Rh factor can only receive negative type blood. Otherwise, there is a chemical interaction that could cause clumping, a stroke, and possibly death.

Your blood type is determined from the shape and function of your red blood cells. The possible blood types are: A, B, AB and O. However there are several different O types.

Type A: The red blood cells have H-proteins attached around the perimeter which bond with the A sugars in your body. These A sugars are made by your body and your body does not make B sugars.

Type B: The red blood cells have H-proteins on their perimeter which bond with the B sugars in your body. Your body makes B sugars but does not make A sugars.

Type AB: The red blood cells have H-proteins on their perimeter which bond with both A and B sugars in your body. Your body makes both A and B sugars.

There are five different type O scenarios.
For ease of explanation we will list them as 1, 2, 3, 4, and 5 but as far as I know they do not have any such distinction.
1) Type O: The red blood cells have H-proteins on their perimeter but do not bond with A and B sugars. A and B sugars are not made by the body.
2) Type O: The red blood cells do not have H-proteins, A sugars are made by the body but do not bond.
3) Type O: The red blood cells do not have H-proteins, B sugars are made by the body but do not bond.
4) Type O: The red blood cells do not have H-proteins, A and B sugars are made by the body but neither bond
5) Type O: The red blood cells do not have H-proteins, A and B sugars are not made by the body and therefore do not bond.

The Rh factor is also accounted for in the make-up of your blood cells. A person is Rh+ if they have Rh located on the perimeter of the red blood cell and Rh- if they do not.

Another interesting facet of blood types is the way that blood types are passed on through genetics. The A and B types are dominant. This means that if one parent passes you the A type and the other passes you the O type, your blood type will be A, just as getting type B and type O will give you type B. If you are given type A from one parent and type B from the other your blood type will be type AB and two Os will result in type O.

There is however one exception to this rule. Parents also pass on H and h, the big H meaning that your red blood cells will have the H-proteins and the little h meaning that your red blood cells will not have H-proteins. If your parents both pass on to you the little h then you will be a type O no matter what A/B/O they pass on to you. The reason for this is that only type O has red blood cells which do not have H-proteins.

Debbie's good writeup above can be simplified in terms of the presence of absence of H substance. If we let capital H represent the normal gene for H substance and little h represent the abnormal gene, then a person can be either hh or non hh (either HH or Hh).

hh is homozygous absence of the gene for H substance -- if you have this you would not produce any H substance - and have the ridiculously rare "Bombay phenotype"

If a person is hh, then his/her blood group is Oh, regardless on what his/her genotype for A or B. If the person is not hh, his/her blood group will depend on the ABO system.

The Bombay phenotype is thankfully rare as anyone with it can be almost assured that it would be supremely difficult finding blood for them if they required a blood transfusion.


Source: Harrison's online.

Canadian Blood Services has prepared a small pamphlet called what's your type? which seems to have its roots in the same Japanese ideas that are so well described by Japanese Blood Type Superstition. They give "most likely occupations" for each blood type:

Type A

Type AB

Type B

Type O

CBS also reports that cats have 4 blood types. They do not indicate how cat transfusions match up, nor if cat blood is interchangable for human. No, let's not try it and see.


* Really. I kid you not.

Statistical distribution of the major blood types in the U.S.:

O+   37.4%
O-    6.6%
A+   35.7%
A-    6.3%
B+    8.5%
B-    1.5%
AB+   3.4%
AB-   0.6%

The rarest blood type found is called bombay blood (subtype h-h), found only in a Czechoslovakian nurse in 1961 and in a brother and sister in Massachusetts in 1968.

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