QUESTION: When my son was 4 years old he was diagnosed as lacking any IgA in his blood. Now, at 15, he is very healthy, but I have some concerns. If he was to need a blood transfusion, would there be a problem? Should he wear a medical alert bracelet? - G.D.

ANSWER: You will have to get some of these answers from your family doctor, who has access to information I don't. But I might be able to clear away some of the haze generally here.Your son has a deficiency of a particular kind of antibody - IgA (for immunoglobulin A). Some people with a serious deficiency of this antibody have recurrent respiratory tract infections and nearly constant diarrhea. Those with a mild deficiency may have no symptoms, and they may even outgrow the condition. Your doctor can advise on this.

Now about blood transfusions: People without IgA make antibodies against it when exposed. Normal blood donors do have the IgA. Thus, if an IgA-deficient person receives blood he could suffer a severe reaction because he has antibodies against IgA. I suggest you have your son checked for the antibodies, to evaluate his present condition and find out if he needs to wear a bracelet or carry a wallet card noting his problem.

QUESTION: My husband is about 60 pounds overweight. He has borderline high blood pressure, which he is trying to control with diet (no salt, etc.). Is there a difference in the size of blood pressure cuffs used for taking pressure? We purchased a kit. Now we hear things like, "If he had his pressure taken with an oversize cuff it wouldn't give the correct reading." Is there a difference in readings if you have a large arm? - A.B.

ANSWER: Yes, the size of the blood pressure cuff relative to the size of the person's arm does influence readings. For those who might not be familiar with it, the cuff here is the inflatable rubber gizmo strapped around the arm, then inflated to gauge pressure in vessels below.

If the cuff is small and the arm too large, the readings will be too high. The opposite combination would produce too low readings.

Now, about the overweight situation. I don't know that his weight is going to change readings very much. But look, tell your husband to take his pressure kit in the next time he visits his doctor. The doctor can check out the readings he gets with those your husband gets with his equipment. Your other blood pressure questions are answered in booklet No. 4 (blood pressure). For a copy, write Dr. Donohue/No. 4, P.O. Box 19660, Irvine, CA 92713, enclosing a long, stamped, self-addressed envelope and $1.25.

C) 1989 North America Syndicate Inc.