Blood Types

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A while ago, Kevin Boyle asked me to write a column about the human blood ABO system and, as I write my columns about two months before in advance, it is appearing today. Human blood types were first discovered by the Austrian physician Karl Landsteiner in the early 1900s, yet even today the function and purpose of the ABO blood type system is unknown. Blood types date back to well over 20 million years ago. Like eye color, blood type is inherited. The letter stands for the type of antigen, or protein, found on the surface of red blood cells. There are two blood proteins – A and B. Someone with type AB blood has both antigens and inherited A from one parent and B from the other. A person with type O blood has no antigens but will have antibodies to both A and B. Likewise, a person who is type A will have antibodies to type B and vice versa. Dogs have four blood types, cats 11, and cows over 800.

The second blood type antigen is the Rh, or rhesus (discovered in rhesus monkeys), factor. In the U.S., 85% of people are Rh +. In China, that figure is 99%. The presence of foreign antigens in the blood activates the immune system to produce antibodies. In newborns, a potentially fatal syndrome may occur called erythroblastosis fetalis. This happens when an RH negative mother gives birth to an RH positive baby. The mother’s Rh antibodies attack the Rh antigens on the baby’s red blood cells. In this country, 37% of people are O+ while 34% are A+. O negative, which has no antigens, is the universal donor while AB +, which has all the antigens, is the universal blood recipient. Because some bacteria closely resemble some blood antigens, the immune system may have trouble differentiating between the two. For example, those with type A are more susceptible to smallpox while type B are more susceptible to E. coli. There are also some minor, mostly insignificant blood types like MN, Diego, Kidd, and Duffy. Of these, Duffy is significant because Duffy negative persons are more susceptible to a malarial infection caused by P. vivax.

There is a theory that blood type is related to personality. This theory states that type A persons are calm and trustworthy, type B are creative and excitable, AB are thoughtful and emotional, and O are confident leaders. In Japan, a person is just as likely to be asked what their blood type is as to be asked what their sign is.

Lastly, blood transfusions are quite common. Prior to a transfusion, a recipient will have their blood type screened twice to prevent an incompatible blood transfusion, except in a dire emergency where O negative blood will be given. Screening both the recipient and donor blood prevents transfusing the wrong blood type, which may result in a transfusion reaction. When given the wrong blood type, a patient may often have immediate symptoms, which is why a nurse will observe the patient at the beginning of a transfusion. Delayed symptoms, which may appear a day or two later, may rarely occur. These symptoms include back or flank pain, dark urine, chills, fainting and dizziness, fever, flushing, shortness of breath, or itchiness. While transfusion reactions are not always serious, they may result in acute kidney failure, anemia, fluid in the lungs (pulmonary edema), and shock.

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 By Peter Galvin, MD

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