DEAR DR. DONOHUE: I read with interest and skepticism your column on prostate cancer and the PSA test for it. Over the years, my PSA test increased, but finger examination of the prostate was normal. Two urologists recommended a biopsy. I read where a biopsy is painful, so I declined. Then, in 1999, I read a book that said the PSA is 93 percent wrong, giving 60 percent false positives and 33 percent false negatives. Why do people continue to rely on a test that is so thoroughly discredited? – C.S.

ANSWER: If you are looking for the 100 percent perfect medical test, you won’t find it. Doctors are aware of the fallibility of the PSA (prostate-specific antigen) blood test for detection of prostate cancer. A reading of 4 is usually taken as a cutoff. Readings lower than 4 generally indicate no cancer, and readings greater than 4 are suspicious for cancer. However, even though a reading of 4 is accepted as normal, 15 percent of men with readings lower than 4 still harbor cancer. Furthermore, it is also true that some men with readings higher than 4 do not have cancer.

Your percentages of its inaccuracy are a bit overblown. If a PSA reading is 2.5 (and that is a normal reading), a man still has a 2 percent probability of having cancer. A reading between 2.5 and 4 – still normal for most men – leaves a man with an 18 percent probability of having cancer. A value between 4 and 10 – no longer normal – gives a man a 25 percent probability of cancer, and one greater than 10 puts a man at a 67 percent chance of cancer. The test is not perfect, but it’s as good a test as we have. Combined with the DRE – digital rectal exam, the finger probe of the prostate gland – it adds important information.

Until there is general agreement that the PSA test is worthless or until a better test comes along, I am sticking with it. Yearly, refinements are made to make the test more accurate.

I think you have been led astray by the statement of the pain involved in a prostate biopsy. The biopsy is uncomfortable, but it is not medieval torture.

DEAR DR. DONOHUE: A year ago, I developed a persistent cough and was given Serevent. This year, I had blood in my sputum and had a CT scan, which showed a thyroid nodule. Could the Serevent have caused it? I am 86. What about cancer? – M.H.

ANSWER: Before death, more than 50 percent of people have developed a thyroid nodule, and few of them took Serevent. That medicine has not been implicated as a cause.

The issue raised by a thyroid nodule is cancer. Only about 5 percent to 15 percent are cancerous. Rapid growth of the nodule, a change in voice quality (the nodule can affect vocal cords) and a very firm nodule that’s adherent to adjacent tissue suggest cancer. Most thyroid cancers appear between the ages of 20 and 60.

If there is any question of cancer in a thyroid nodule, scans help settle that issue, and biopsies of suspicious nodules with a very slender needle retrieve cells from them. Those cells are subjected to careful microscopic examination to detect any cancer changes.

The thyroid booklet covers the more common thyroid disorders but not thyroid cancer. Readers can obtain a copy by writing: Dr. Donohue – No. 401, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: Please clarify when we retirees need a pneumonia booster shot and how often. I had a shot prior to my retirement in 1994 and a booster shot in 1998. When do I need an additional booster shot? I am currently 73. – D.M.

ANSWER: The “pneumonia” shot is a vaccine for one kind of pneumonia – pneumococcal (NEW-moe-KOK-ul) pneumonia, the most common kind of bacterial pneumonia and one that can be deadly for older people.

At present, only one shot is recommended after age 65 (some would say age 50). If a person had the shot before age 65, and if five or more years have elapsed since that shot, then a second vaccination is recommended.

This recommendation is subject to change as new information is obtained.

Others – those with impaired immunity, for example – need the vaccine and booster shots and at younger ages.

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. Readers may also order health newsletters from www.rbmamall.com.