What the Test Results Mean
To repeat, the HIV test is designed to determine the presence of HIV in- fection—that is, it is designed to detect antibodies to the virus. Antibodies to the virus are present in virtually all people who are infected and absent in people who are not infected.
Test results are usually either positive, meaning the antibodies are present, or negative, meaning they are absent. Occasionally test results are indeterminate, meaning that the results were neither clearly positive nor clearly negative. In this case, the test should be retaken.Inaccurate or false test results are extremely rare. Nevertheless, as discussed above, the test is not always positive in people who are infected and not always negative in those who are not infected.
Negative Test Results
A negative result of the test generally means the virus is not present. In rare cases, as noted above, the negative result can be false. This can happen if the test is taken during the three-to-four-week period (or occasionally longer) between the time of infection and the time when antibodies develop. For the person who is concerned about false negative results, the usual recommendation is to repeat the blood test after two to three months.
Indeterminate Test Results
The virus is either present or not present—there is no middle ground. But like all tests in medicine, the test for antibodies to HIV does not always give decisive positive or negative results. Indeterminate test results are a gray zone, and they are an obvious source of anguish for the person tested. They could mean that the person is early in the course of infection and in the process of manufacturing antibodies to the virus. Or they could mean that the body has produced some miscellaneous protein that is unrelated to HIV. Or indeterminate results could mean that the body has produced antibodies to a virus related to HIV but still somewhat different.
Certain rare strains of HIV in Africa are occasionally seen in the United States. These rare strains, known as HIV-2 or type M, don’t give clear-cut results on the standard HIV test. Most rare strains turn out to be HIV-2, for which we now have tests.People with indeterminate results are usually told to be tested again in two to three months. If the person with an indeterminate result has been exposed to the virus recently, the results of the second test may be positive. If the person has not recently acquired HIV infection, the results of the second test are usually indeterminate again. The reason for this is unknown. Almost invariably, however, these people do not have HIV infection. The indeterminate results are never explained and have no consequences.
As noted above, alternative tests may be used to detect the virus instead of antibodies to the virus. These tests, however, are not as well standardized as the antibody tests.
The usual recommendation is to repeat the test for antibodies in three months. While all this gets sorted out, the person being tested is advised to take precautions to prevent transmission, just as if the test were positive.
Positive Test Results
A positive test means that antibodies to HIV are present. If the antibodies are present, the virus is also present. The person with positive results can transmit the virus to others and needs regular medical attention and access to therapy.
Over 99 percent of the people with positive tests know how they became infected; for a small portion of people, the source of the infection is unknown or claimed to be unknown. Because false-positive tests occur occasionally (rarely), the person with a positive test who has no reason for it may request that the test be repeated. People with a positive test will understandably be upset, will need psychological counseling, will need medical care, will need to know how to prevent transmission, may need ongoing psychological support, and will certainly need the support and friendship of the people they love. All this, of course, is what this book is about.