blood types

The subject of blood types is a constant source of confusion to patients. Parents are often anxious because they do not know their children's blood types, afraid that in some way this might jeopardize their care in an emergency situation. This is a groundless fear; if the blood type is ever needed, it is obtainable in a couple of minutes in the lab.

The blood groups of humans are listed for your edification and amusement; they are listed in descending order of frequency in the population:

Type O
Type A
Type B
Type AB
And the Rh (Rhesus Factor) type, which is either positive (present) or negative (absent). Rh factor positive people are more common than Rh negative people.

The system works like this: a person receives one blood group gene and one Rh factor gene from each parent. The blood group gene can be either type A, B, or O (which is actually simply the absence of either type A or B, a point of some additional confusion). These genes determine what markers (antigens) are present on the surface of the blood cells. A cell may carry the A antigen, the B antigen, both A and B, or neither (that is, Type O).

Blood types are generally of no consequence in life or even in medicine unless a person needs to receive blood (or be a transplant donor or recipient, to get rather far afield here). Knowing your child's blood type does almost no good in the real world. If your child were ever in an accident and needed blood immediately,

The doctor wouldn't take your word for it - she would do a blood typing test as part of selecting the blood to transfuse
A crossmatch test would verify that your child's blood and the donor unit were not dangerously incompatible
If you wanted to donate blood directly to your child in an emergency you couldn't do it - it would take too much time to process your donation and your child would still get someone else's blood - a volunteer donor unknown to you. Of course, the blood bank would be very grateful if your family repaid the debt by donating blood for others in similar need as your child.

Another broad area of misunderstanding is of course the issue of determining paternity by blood types. This is essentially no longer used now because more sophisticated and accurate DNA tests are used.

The only time we routinely do blood types on children is when they are born, and in most hospitals, only if the mother is type O or is Rh factor negative.

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