Treatment Review #18; April 1995

Researchers are still looking for a good marker or group of markers that help clinicians and people with HIV to make appropriate decisions about what treatments they should or should not take. Measurements of the amount of virus in the blood may be a useful tool that will help make these decisions.

Two new tests measure the amount of HIV in the blood, sometimes called the viral load. Both of these tests are done by taking a blood sample, then performing tests on this blood in a laboratory. The blood is discarded after it is measured. It is not returned to the person from whom it was taken.

One test, called the branched DNA or bDNA test, is made by a company called Chiron. The other is the polymerase chain reaction or PCR test made by Hoffman-LaRoche. The two tests measure what's called HIV RNA. RNA is the part of HIV that knows how to make more virus. Scientists have a good idea what some parts of HIV RNA look like. By creating a mirror image and matching it against what they find in someone's blood, they can find HIV RNA.

The PCR test encourages the HIV RNA to make more of itself so that it's easier to measure, then works out how much HIV RNA must have been there in the first place. The bDNA test sets off a chemical reaction with the HIV RNA so it gives out light. Then the amount of light is measured in order to show how much RNA was found.

The number of copies of HIV RNA in the blood can go from less than 10 into the hundreds of thousands. Studies have shown that the amount of virus in the blood increases as someone gets sicker. Some treatments can reduce the amount of virus in the blood. Whether this will improve someone's health isn't clear, because studies haven't been done that prove this.

The results of these tests are usually given per milliliter (ml) of blood, like the T4 cell count. The PCR test may give the amount per 0.05/ml, so you need to multiply the number by 20 to get the standard result. Each virus carries two copies of RNA. If there are 100,000 copies of HIV RNA, that means 50,000 viruses (often called particles or virions) are present. Currently, the bDNA test can't find less than 10,000 copies of HIV RNA, but a recent improvement means it will soon be able to find anything down to 500 copies.

Test results can be different when repeated on the same blood sample. This is called variability. Any test results should say how variable the test might be. For example if the result was 20,000 copies and the variability of the test was 5,000, you'd know that the result was somewhere between 15,000 and 25,000 copies.

Researchers hope these tests will help show if an anti-HIV treatment is working. They also hope the amount of virus in the blood may indicate if someone should start or change to a different anti-HIV treatment. Some doctors feel that there is already early evidence that reducing the viral load will improve health. Others point out that there is a lot of virus in other places in the body, not just the blood. Only 2% of HIV is in circulating blood. The rest is in your lymph system and other body tissue. Also, measuring the good effect an anti-HIV treatment has on the viral load doesn't take into account any bad side-effects the treatment might have on the body.

Currently, these tests are still experimental. Doctors can order them, at a cost of about 200 dollars. However, it's hard to get an insurance company to pay for them. Medicaid will not cover them. Some research studies measure viral load, but people in the study may not always be able to see the results. If you're thinking of joining a study and want to know the results, ask the study coordinator if you will be able to get copies.

It is expected that researchers will soon have a better idea of what these tests mean. Until then it seems a good idea to be cautious when looking at any results of these tests. The labs that do the tests can be asked to provide a chart showing the first test result and any changes over time. This may give extra information about a persons health. It will require further studies to show how this information should be used when thinking about treatment.

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