Viral Load or Viral Burden refers to the amount of virus present in the blood.

RNA is the genetic material of HIV. Measuring the genetic material of the virus is the most direct way to measure the virus. The (Amplicor) QC-PCR (Quantitative Competitive Polymerase Chain Reaction) HIV RNA test can detect down to 400 copies of RNA per millilitre of plasma, and ultrasensitive tests can detect viral load levels between 50-400 copies. While it only measures the virus level in the blood, it is believed to be a good indicator of the amount of virus in the entire body.

Viral load testing is used along with T-cell (CD4) counts to help monitor the status of HIV disease and predict its future course. A low value for viral load can indicate a slower disease progression.

Viral Load tests are reported as the number of HIV "copies" in a millilitre of blood. The test can detect 50 copies at the lower end and at the upper end 1,000,000. (This is reported as e.g. 10,000 = 10 ⁴). A high Viral Load - greater than 100,000 copies, indicates a higher risk of disease progression. A low viral Load - less than 10,000 copies, indicates that risk of disease progression is relatively low in the near future. An "undetectable" test result indicates that the test is not sensitive enough to find small amounts of virus.

Viral load tests can help to determine when anti-viral therapy (combination drug treatment) should be started and how effective the present combination anti-viral drugs are. If considering starting drug treatment this decision should not be made on a single viral load result. A single result is not a good indication of your present immune status.

Initially it is a good idea to have two tests at separate visits. This will give a reliable measure of the baseline HIV level. To evaluate anti-viral therapy, a viral load test should be carried out two to four weeks after it is started. As monitoring therapy a viral load test should be performed every three to four months to confirm that the anti-viral regime is effective. An illness or certain vaccinations can affect viral load test results.

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