DEAR DR. DONOHUE: Should a person try to lower a fever? My mother always had me take aspirin when I was a child and had a fever. Now I react to fever just as my mother did. I always give my family aspirin when someone has one. Is this a good idea? – F.G.

ANSWER: Authorities have a hard time defining what a fever is, and they have a harder time advising what to do about one. Most define it as a temperature greater than 99.5 F (37.5 C) together with other signs and symptoms of illness. The latter is important because some perfectly healthy people have a slightly elevated body temperature. Furthermore, there is a daily variation in body temperature, with its nadir occurring at 6 a.m. and its high point about 10 to 12 hours later.

The body rarely reacts in ways that are not to its benefit. A fever, therefore, might bestow an advantage in containing invading germs and in bolstering the immune system. However, proof that it is advantageous is not overwhelming.

Neither is there overwhelming proof that it is necessary to lower a temperature in most instances. Higher body temperatures increase body metabolism and make the heart beat faster. People who are on the brink of heart failure might benefit from lowering an elevated temperature. The same holds for people whose lungs are not in tiptop shape. There is something to be said for lowering fevers in people who are prone to seizures. For everyone else, however, there is no pressing need to pass out medicines to bring down body temperature.

If a fever makes a person uncomfortable, then lowering it makes sense. When giving temperature-lowering medicines like aspirin and Tylenol, they should be given on a regular basis according to directions on the bottle. If they are given only on an as-needed basis, when their effects wane they can cause hectic fever spikes and drenching sweats. Aspirin should not be indiscriminately given to children whose temperature is elevated from viral infections, for fear of ushering in Reye’s syndrome.

DEAR DR. DONOHUE: My 20-year-old daughter wound up in the hospital with blood clots because of birth control pills. During her hospitalization it was discovered she has something called factor V Leiden and should not take the pill. What is the significance of all this? – V.P.

ANSWER: Factor V (factor 5 – V here is the Roman numeral for 5) is a blood protein that aids in clot formation. Factor V Leiden is a genetic change that occurs in that protein and makes the possessor produce clots when there is no call for them.

Your daughter should never take birth control pills. She must avail herself of other forms of contraception. Birth control pills slightly increase a normal woman’s risk for forming clots. For a woman with factor V Leiden, the pills greatly increase the risk for inappropriate clots.

What to do for your daughter is a matter of debate. She should remain on blood-thinning medicines for at least six months. Whether to continue with them for life depends on how serious her recent episode with clots was and whether she has two factor V Leiden genes. A person with one such gene has a five- to tenfold increase in the risk of a clot; a person with two genes has a fifty- to hundredfold increase in the chances of having a dangerous clot.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.

DEAR DR. DONOHUE: I take three blood pressure medicines. I check my own blood pressure twice a day with my own blood pressure machine. It is never higher than 85 over 50, and sometimes it is a lot lower than that.

I am constantly tired. I think the reason is my blood pressure. Do you agree? – R.M.

ANSWER: Low blood pressure can be healthy, but low pressure with signs and symptoms is not healthy. Your constant fatigue could well be due to your low pressure.

Call your doctor. I am certain that he or she will change your medicine or have you stop one of the three you are now taking. Don’t do it on your own. You don’t know which one is the best one to stop.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.