The Human immunodeficiency virus (HIV) viral load test provides important information that is used in conjunction with the CD4 cell count:
- to monitor the status of HIV disease,
- to guide recommendations for therapy, and
- to predict the future course of HIV.
Evidence shows that keeping the viral load levels as low as possible for as long as possible decreases the complications of HIV disease, and prolongs life and reduces transmission of the virus to others. For this reason, treatment of HIV is currently recommended for all individuals infected with HIV regardless of their viral load or CD4 counts.
There are several methods for testing viral load; results are not interchangeable so it is important that the same method and the same laboratory be used each time.
A viral load test is ordered when a patient is first diagnosed with HIV. The test result functions as a baseline measurement that shows how actively the is reproducing and whether treatment is immediately necessary.
If and when therapy is started or changed, your doctor should request a viral load test and a CD4 count to evaluate whether therapy is being effective. To monitor long-term therapy, it is recommended your doctor request viral load tests and CD4 counts every 3-6 months.
Viral load tests are reported as the number of HIV copies in a millilitre (copies/mL) of blood. If the viral load measurement is high, it indicates that HIV is reproducing and that the disease will likely progress faster than if the viral load is low. A high viral load can be anywhere from 5,000 to 10,000 copies and can range as high as one million or more.
A low viral load is detectable but less than 500 copies, depending on the type of test used. This result indicates that HIV is well suppressed by your immune system. For patients on anti-HIV therapy the goal is to have an undetectable viral load. If your viral load is persistently detectable on treatment, it may mean that the therapy is not being taken correctly (i.e. some doses were missed) or that the therapy needs to be changed because the virus has developed resistance.
A viral load result that reads 'undetectable' does not mean that you are cured. It means that the level of HIV virus in your blood is below the threshold needed for detection by this test. Most viral load tests used in Australia have a lower limit of detection of HIV virus between 20-75 copies/mL. Regardless of blood viral load, HIV is still present, “archived”, in lymphatic tissues and will re-emerge if treatment is stopped.
Change in viral load is also a very important measurement. A rising count indicates an infection that is getting worse, while a falling count indicates improvement and suppression of the HIV infection. However due to variability inherent in the test measurements a threefold change in the viral load copies/mL is required before the change can be considered significant.
A non-infected person should have no circulating HIV virus in his or her blood and, therefore, a negative or undetectable viral load.
Viral load testing should not be used for diagnosing HIV; the HIV antibody test is still the preferred method of choice for this.
Viral load testing done by the PCR method is incredibly sensitive, which can give rise to results.