ATIS would like to acknowledge the AIDS Clinical Trials Group for their contribution.
Because viral load testing is an integral part of the management of HIV disease, it is important to learn what this test is and how it is used. Trying to understand viral load testing isn't easy. This fact sheet was developed to help clarify information about viral load testing.
Another consideration for measuring viral load is cost. Because the test is expensive (tests can range between $63-$292 with a commonly reported cost of $200 per test), it is important to have them drawn at appropriate times.
Using the same starting point of 20,000 copies/ml plasma, a 1 log decrease means that the viral load has dropped to 2,000 copies/ml. A 2 log decrease equals a viral load of 200 copies/ml plasma. An easy way to figure out log changes is to either drop the last "0"or add "0"to the original number.
Any change of less than one-half log is considered insignificant. More simply, if the viral load measurement has not tripled or dropped to one-third of its previous level, the difference might be unimportant. For example,if the baseline viral load were 20,000 copies, a rise to 60,000 or a fall to 7,000 copies might just be the result of transient changes. Repeat testing of a single specimen may give two quite different results and natural biological day-to-day variability of samples from the same person may cause measurements to vary slightly. Researchers believe that clinical decisions made on the basis of changes in viral load ideally should be based on measurements taken 2-3 weeks apart.
What Does An "Undetectable" Level Mean?Many individuals now have an "undetectable" level of virus in their blood after taking combination therapy. "Undetectable" levels do not mean that the person is "cured" or no longer infectious. "Undetectable" levels mean that current tests are not sensitive enough to measure very low levels of virus in the blood, for example less than 400 copies/ml. There are experimental assays used in research which are more sensitive and can detect levels of virus as low as 20 copies/ml but they are not generally available in clinics and doctor's offices.
Even if the measurement of virus is less than 20 copies/ml in the blood, HIV may be present and infectious in blood, genital secretions (such as semen), lymph nodes, other lymphoid tissues, and elsewhere in the body. There are insufficient data to say that individuals with "undetectable" levels of virus are no longer infectious or no longer at risk of disease progression in the future. We simply do not know yet what an "undetectable" level of virus means over the long term. Individuals with "undetectable" levels of virus still need to be monitored by their health care providers regularly and they need to practice risk free behaviors.
Is There Still a Need to Have CD4+ Levels Monitored?Even with ongoing monitoring of viral load, it is important to monitor CD4+ levels. CD4+ levels provide information about the status of the immune system. Research has shown that when viral load is lowered, CD4+ levels usually increase. However, research is still ongoing to determine whether the increase in CD4+ levels represent normal, functioning immune cells. CD4+ levels continue to be used as the basis for deciding what type of opportunistic infection prophylaxis a patient should take. Some physicians feel decisions about prophylaxis should be based on the lowest CD4+ level recorded for a person. CD4+ cell levels are also used to measure response to antiretroviral treatment, although most regard viral load as more important indicator. In order to provide the physician with the best possible information about a patient's disease status, it is important to have routine viral load and CD4+ levels measured.
Additional InformationFor additional information about viral load testing or other treatment issues, contact:
HIV/AIDS Treatment Information Service
To order a print copy of this publication (Inventory No. D523), call or email the HIV/AIDS Treatment Information Service.
This article was provided by AIDSinfo. Visit the AIDSinfo website to find out more about their activities and publications.