I need to be tested for AIDS. Where can I go to get this done in confidence? How much does it cost?

C.A.

Yours is one of the most common medical concerns that I hear. First, you should understand that the test you are considering does not detect AIDS (acquired immune deficiency syndrome) per se. Rather, it looks for exposure to HIV (human immunodeficiency virus). Severe infection with HIV causes AIDS, a characteristic group of infections and tumors.

When you get an HIV test, your blood will be sent to a lab for an exam called ELISA, which looks for infection-fighting antibodies against HIV. The test is very "sensitive," which in scientific terms means that the test will come up positive in almost everyone who has HIV. The exception is among people who are tested soon after being infected, typically less than two months. In them, the ELISA test may fail to find any antibodies, and the result will be erroneously negative.

Although the ELISA test is unlikely to miss a person who does have antibodies to HIV, it may sometimes report a "false-positive" finding -- that is, it will say that someone has HIV antibodies when they really do not. For that reason, every positive ELISA test is confirmed with a second test, usually one called a "Western Blot." This test also looks for antibodies, but it has very, very few -- if any -- false-positive results.

What do I suggest for you? I think the best way to be tested is by your own physician. Your doctor is probably the best person to counsel you before and after the test. When I counsel a patient, I explain how the test is performed and that testing positive for HIV is not the same thing as having AIDS, because people who are HIV-positive will likely have many years of good health. I also explain that excellent treatments are available, and that if the test is positive I will be with the patient every step of the way for his or her future medical needs. Once the result comes back, if my patient tests positive, I reassure him or her that there is still a lot of hope -- which there is! If the patient tests negative, I remind him or her that the good result is not a free ticket to behave in a risky way in the future. I explain that HIV infection could occur at any time if the patient continues unsafe practices.

Now, about the confidentiality issue: I would like to tell you that all physicians are perfect when it comes to maintaining confidentiality, but it is not true. Most doctors are very good about it, but not all of them. You also may also have legitimate concerns about the confidentiality of your doctor's staff.

So, here is what I suggest: If you trust your doctor, ask him or her to test you. If you do not trust your doctor, consider getting a new one. Seriously, you should have complete trust in your physician. However, if you want to avoid getting tested by your own doctor, most cities have public health offices that will test you for free. I have never heard of a breach of confidentiality at a public health office. Finally, in the United States, every medical practitioner has to report positive HIV test results to the U.S. Centers for Disease Control for study purposes, but the names are replaced by codes for confidentiality.

Another way to get tested is with a home HIV-testing kit. Following the directions on the kit, you send a small sample of your blood to a lab. You put a number, not your name, on the sample when you send it in, so you are completely anonymous. Later, you call a toll-free number and get a short counseling session and your result. I would prefer that you see your own doctor, however, because getting news like this over the phone is too impersonal.

As to cost, most doctors' lab charges are about $40 (U.S.). The kit costs about the same amount. Most public health offices test for free.

As a final note, DO NOT donate blood for the sole reason of getting an HIV test. Donated blood is screened for HIV, but the screening tests are not perfect. If lots of people donate blood because they think they are at risk of HIV, the amount of tainted blood in the pool of donations will increase, and that makes it more likely that some infected blood will be missed by the normal screening methods. In addition, some of the people who donate will be in the "window period" before antibodies to HIV show up. Their blood is highly likely to escape detection and be given to an unwitting recipient.