Are You My Type?

That depends. Are you negative? Or positive? And what are your initials? A? B? Or, perhaps, O?


Just what is blood type, anyway?


Blood type is a classification system based on antigens. Antigens are substances that cause the body to produce antibodies. Antibodies then set out to destroy the antigens. In a way, antigens are irritants that cause a reaction. Think of getting a stone in your shoe. The stone is an antigen. It causes you to do something to get rid of it. Your brain mobilizes your arms and hands to get rid of the stone. Your arms and hands are the antibodies. But imagine that the stone is a burr. You get the same reaction: brain – arms – hands. But now the burr “fights” back. It pricks your finger as you try to pull it off. This causes your hand/arm to withdraw. Then the process begins again until either your hand or the burr “wins”.


So blood is classified according to the type of antigen it carries on the red blood cells. Type A carries the type A antigen on the red cells. Type B carries B. Type AB carries both A and B. Type O carries no antigen on its red cells.


The red cells carry hemoglobin. The hemoglobin is what makes blood red. The role of hemoglobin is to carry oxygen to the body. That’s why oxygen-rich blood, which is in arteries, is bright red while oxygen-poor blood, found in the veins, is dark red. The liquid part of the blood in which the cells float is called plasma.


Plasma contains the antibody. Type A blood plasma has antibodies against Type B blood. Type B blood has antibodies against Type A blood. Type AB blood plasma has no antibodies. Type O blood has antibodies against both Type A and Type B.


Are you negative or positive?


This refers to the rhesus (Rh) factor. This is another antigen that is on the red blood cells. If it is present, the blood is positive. If it isn’t present, the blood is negative. Blood of any type is either Rh positive or Rh negative.


Why is blood type important?


Blood type is important during pregnancy, after major blood loss and in diseases that require transfusions, such as hemophilia and Sickle Cell disease.


For a blood transfusion to cause no harm (that hand/ burr fight), the blood to be given to the recipient must NOT cause the recipient’s plasma to attack it.


Type O was once called the universal donor blood and Type AB the universal recipient. Type O has no antigen so it will not cause the recipient blood to attack it; AND the amount of its anti-bodies (both A and B) is not large enough to successfully mount an attack against the recipient’s blood. Type AB has no antibodies so it’s not going to fight off any blood.


As researchers have discovered more about blood, the idea of a universal donor or recipient has undergone change and is no longer in common use.


In pregnancy, the fetus acts as a foreign body. Usually pregnancy related hormones eliminate this reaction. However, if the mother’s blood is Rh negative and her baby is Rh positive, the mothers’ blood will try to attack the baby’s blood. This does not happen with the first Rh positive pregnancy. The antibodies are just stimulated by the first pregnancy into being on guard against another Rh antibody attack. However, the second and following Rh negative babies will be treated as foreign bodies. This can kill the baby or cause life-threatening problems shortly after birth.


Today a drug is given to an Rh negative mother after the birth of her first child, so that this Rh incompatibility will not occur.


So, will you be a burr in my blood stream? Will my plasma fight your red calls and cause them to die and clump in my veins and arteries? Are we a good match or not?


Since blood type is inherited, I guess you’ll just have to blame any incompatibility on your parents.


Mary Lou Bernardo, PhD, MSN


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