Viral load tests can give important information about the disease status of HIV-infected people. These tests measure the amount of HIV circulating in the blood (sometimes referred to as HIV RNA). By measuring viral load, we get a picture of how active HIV is. The combined use of viral load and CD4+ cell count test results can help give a clearer picture of your stage of HIV disease and help develop a personal treatment strategy. A good way to think about these tests is that the CD4+ cell count provides a measure of immune health, whereas viral load provides a measure of how active the virus is.

There are two viral load tests commercially available: Q-PCR (called "PCR" or Amplicore^®) and bDNA (called Quantiplex^®). Although the Q-PCR test is as yet the only federally approved test, both versions are widely used. Both tests take a sample of blood and calculate the number of viral particles present in the blood sample. In general, the Q-PCR test is the most sensitive and can detect low levels of virus in the blood, whereas the bDNA test has been shown to be the most accurate for detecting high levels of virus. It's important to stick to the same test over time to get an accurate account of changes in viral load.

The How and Why of Testing

Initially, two viral load tests should be performed at 2-4 weeks apart to establish a "baseline" level. Using two tests to set the baseline helps rule out lab error. Lab errors can happen with any test, and it's important to ensure your initial treatment decisions are based on accurate information. If either test result differs by more than 100% from the other, it's a sign that one of them may have been in error. In this case, it's often recommended getting a third test to see which one of the earlier tests was more accurate. Afterwards, tests should be repeated every 3-4 months along with CD4+ cell counts. Ask your doctor for a copy of your test results. You are entitled to them.

Viral load tests are used most commonly for two different purposes. First, they are used to help patients and physicians determine the appropriate time to start treatment. The combined results of viral load testing and CD4+ cell count tests provide important input on this question (though they are not the only factors to consider). Secondly, viral load testing is commonly used to measure the effectiveness of treatment. If a treatment regimen is working, it should result in a rapid reduction in viral load. When it fails to do so, this is usually an indication that different drugs might be needed.

Interpreting the Results

Viral load test results can be difficult to interpret. A few general guidelines are provided here, but they may change as more research is done and newer tests become available.

Viral load results are usually given as the number of HIV RNA "copies" in a milliliter (ml) of blood (about a teaspoon). As with CD4+ cell counts, what is most important is the trend of your viral load test results, not just the individual result. Changes in viral load are considered "significant" when they show a three-fold difference from previous results (this means three times larger or smaller than the last result). For example, a viral load test that goes from 20,000 to 30,000 is not considered significant, but a change of 20,000 to 70,000 is. This is because viral load levels can vary from day to day due to a variety of factors, including other active infections (flu, herpes, and sinusitis), vaccines, stress, malnutrition, and error level of the test.

Viral Load Testing: Interpreting the Results

Low, stable and/or decreasing viral load level is considered a good thing. A high or increasing level warrant attention. High or increasing viral levels for someone on anti-HIV therapy may indicate the development of drug resistance. Low viral load: generally below 10,000 copies/ml. This result indicates that HIV is not actively reproducing and that the risk of HIV progression is low. High viral load: above 100,000 copies/ml. This result indicates a higher level of viral activity and thus a higher risk for HIV disease progression. Remember to consider CD4+ cell count. The combined test results give a more accurate indication of risk for HIV disease progression than viral load results alone. When CD4+ cell counts fall below 50, the usefulness of viral load levels as a predictor of disease progression declines. Rather, the CD4+ cell count becomes the most reliable predictor. Remember: a single test does not make a trend! There is a great deal of natural variability in most test results, so you should avoid panicking if you happen to see a number you don't like. Generally, any time you get what appears to be an alarming result, the next step should simply be to repeat the test to determine its accuracy. Most physicians discourage people from making changes in their therapy based on any single test result. Instead, it is the change over time that should guide treatment decisions.

Undetectability: To Be or Not To Be?

Viral load levels which fall below the level at which tests can measure them have been called "undetectable." This does not mean that the virus is not there, but only that it is present in too small of an amount for the test to pick up. The Q-PCR test cannot accurately measure levels of fewer than 400 copies of HIV RNA in a blood sample. Newer "ultrasensitive" tests like the Ultrasensitive PCR test can accurately measure as little as 20-50 copies of HIV RNA. As these ultrasensitive tests become more available, people with results falling below the limit of detection on earlier tests may find they suddenly have detectable viral loads. This would not necessarily mean that viral load has increased, but rather that more advanced technology is better able to measure lower levels of virus.

Viral load testing has provided us with a great tool for monitoring HIV disease and the effectiveness of anti-HIV treatments. At the same time, it can be an added stress! For many people, viral load tests can take a psychological toll: if the test results are good -- which is often interpreted as undetectable -- you feel great; if they are "bad" -- you feel horrible.

The goal of "undetectability" can add to this stress, especially as the level of detectability decreases. Whether 400 copies/ml or 20 copies/ml, some people may never reach an "undetectable" HIV viral level. It's important to remember that being "detectable" does not necessarily mean HIV is progressing or treatment is not working. Talk to your doctor about what your HIV viral level results mean about your health.

Getting Viral Load Tests

Both Roche and Chiron, the companies that make Q-PCR and bDNA respectively, offer Patient Assistance Programs to supply their tests free-of-charge to people who have no other means to pay for them ($150-250 each). The availability of these programs may be limited geographically, but you can call the following numbers for more information:

Chiron (bDNA): 1-888-HIV-LOAD (448-5623)

Roche (Q-PCR): 1-888-TEST-PCR (837-8727)

Both tests are FDA-approved and most insurance providers and Medicaid will pay for tests once the FDA approves them.

For more information on viral load and other tests for monitoring HIV, ask for Project Inform's Diagnostics Fact Sheet.