Ever Wonder About Your Blood Type?

By Howard J. Bennett

No one likes to have his blood drawn, and that is especially true for kids. As soon as I greet one of my patients for a checkup, I get asked two questions. First, “Do I need any shots?” Second, “Do I need any blood tests?”

I am always honest with my patients, but it’s not a good idea to talk about needle pokes at the beginning of a visit. I deal with this by telling kids that a doctor’s visit has three parts: the talking part, the examination part and (sometimes) the getting poked part. I remind them that I won’t know the answer to their question until we get to Part 3.

The most common blood test doctors do is a CBC, which stands for complete blood count. The test provides information about red blood cells, white blood cells and platelets. We do CBCs for different reasons, but the two most common are to check for anemia (red blood cells) and infection (white blood cells). Platelets are the element in blood that helps it clot if you become injured.

Lots of kids ask me what their blood type is. When I tell them that information isn’t important on a day-to-day basis, they look puzzled. So here’s the skinny on blood types.

The basic blood groups everyone knows about are A, B, AB and O. In addition, blood can be “positive” or “negative.” (This relates to something called the Rh factor.) O positive is the most common blood type among all ethnic groups. AB negative is the least common.

The type of blood you have refers to markers on red blood cells—like the street numbers on your house—that allow your body to recognize itself. Except for people with AB positive blood, everyone has proteins in their body called antibodies, which alert the body to blood types that don’t match. Getting transfused with mismatched blood can cause serious reactions. (A transfusion is a procedure where a sick or injured patient receives blood into his veins that’s been donated from another person.)

What most people (even parents) don’t know is that we also have minor blood groups in our system. That basically means that not all A positive blood is the same. Minor blood group mismatches don’t usually trigger serious problems, but they can cause mild transfusion reactions, which should be avoided.

If a person needs a transfusion on an emergency basis, he will always get O negative blood even if his blood type is A positive. That’s because O negative blood has no markers that warn the body that the blood doesn’t match.

You may have heard doctors on TV shows shout the following order to the closest nurse: “Type and cross the patient and get me six units of O negative blood, STAT!” (STAT is doctor talk for immediately.)

“Typing the patient” means finding out what type blood he has. “Crossing the patient” means comparing his blood with similar blood types available in the blood bank. That way, the patient will get the best A positive blood on hand, including the minor groups.

© 2013 Howard J. Bennett. All Rights Reserved.
(First published in the Washington Post 6/24/13.)

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