Viral Load Testing

Viral load testing measures the amount of new virus being produced and released into the bloodstream. Several studies have shown that higher levels of viral load are associated with more rapid disease progression and a greater risk of death. Lower levels are associated with stability and reduced risk of progression, infection, or death. Ideally, an HIV infected person should have no detectable level of virus, which means that the level of virus activity is too low to be measured. Currently available tests measure down as low as 200 to 500 copies of virus, the lowest amount presently measurable. This is associated with the best possible clinical outcome. Higher levels, ranging from several hundred upwards of millions of copies of virus, are associated with higher rates of disease progression. In short, the higher the number, the more rapid the rate of disease progression.

Clinical trials of new drugs use these tests to measure the effect of drugs. A good antiviral drug can quickly reduce the level of virus at least ten fold and often as much as a thousand fold. The goal of  therapy is to reduce the viral load to the lowest level detected by the test, usually below 200-500 viral copies.

HIV infected people and their physicians use these tests to make decisions about when and if to use antiviral drugs, and to determine if a drug is working on not. When the virus levels begin to rise again while using a drug, most physicians believe it is time to switch to another drug or combination of drugs.

Recent studies have resolved most doubts about the use of these tests and it is likely that reimbursement for them will improve greatly. At the very least, the test provides a rational basis for deciding when or whether to use antiviral drugs, as well as a tool for determining whether or not an antiviral drug is working.