What is a plasma viral load test?
A plasma viral load test (also called a PVL test) measures how much human immunodeficiency virus (HIV) is in your blood. The amount of HIV in your blood is called your "viral load." The lower the viral load, the less amount of the HIV virus.
If your doctor knows your viral load, he or she can tell more about your risk of health problems caused by HIV infection. A PVL test helps your doctor determine if your current method of treatment is working or if it is time to change to different medicines.
Who needs a PVL test?
PVL tests are intended for people who have already been diagnosed with HIV or acquired immunodeficiency syndrome (AIDS). This kind of test can help your doctor monitor how efficient and healthy your immune system is. Regular PVL tests can also help you and your doctor make decisions about which treatment is right for you and when to start it.
Because PVL tests can detect HIV faster than other tests, they're also used in newborn babies whose mothers have been diagnosed with HIV or AIDS. If test results show that HIV is present in the baby's blood sample, doctors can start treatment sooner.
Pregnant women who may have had a recent exposure to HIV can also have a PVL test. This test can help them make informed decisions, such as when to start treatment to avoid infecting their baby with HIV.
PVL tests are not designed for people who want to know their HIV status. There are other tests that are cheaper and more reliable for telling whether a person has HIV or not.
What do the results mean?
Results of PVL tests are usually given as "copies per milliliter (mL)" of blood. PVL tests measure how much HIV RNA is in a sample of your blood. RNA is the "blueprint" that HIV uses to make more of the virus. Each HIV virus carries 2 copies of RNA. This means that if there are 20,000 HIV RNA copies per mL on your test report, 10,000 virus particles are present in each mL of your blood.
The amount of HIV in your blood may change. Changes in PVL are often called "log changes." A log change means that your viral load is 10 times more or 10 times less than a previous PVL test result. For example, if a PVL test showed that you had 20,000 HIV RNA copies per mL, a log change would be either an increase to 200,000 copies per mL or a decrease to 2,000 copies per mL. The goal of HIV treatment is to get your PVL results as low as possible.
Most doctors consider a viral load of 500 or fewer HIV RNA copies per mL low, while a viral load of 40,000 or more HIV RNA copies per mL is considered high. Before your doctor makes decisions about your HIV medicines, he or she may want you to have 2 PVL tests done 2 to 3 weeks apart to monitor changes.
How does a PVL test help my doctor decide when to start HIV medicines?
If you have not started taking medicines for HIV infection, your doctor will probably want to test your PVL several times a year to see if the amount of HIV in your blood is changing.
Your doctor might think about starting you on HIV medicines if your PVL is higher than 10,000 to 30,000 copies per mL. This is a complicated decision to make. Your doctor has to think about any other medicines you are taking and the other health problems you may have. The same PVL test result may lead to different decisions for different people.
Your doctor may also want to check your CD4 lymphocyte cell count. The CD4 cells are white blood cells that help the body fight infection. They are the cells that HIV attacks. The CD4 cell count helps to show how healthy your immune system is (a high CD4 count means a healthy immune system). When the PVL test score goes down, the CD4 cell count usually goes up, although this might take some time. CD4 cell counts can also help you and your doctor decide when to start or change HIV medicines.
How are PVL tests used during HIV treatment?
If you are already taking medicines to treat HIV infection, your doctor will want you to have a PVL test several times a year to make sure that the medicines are working for you. If your PVL goes up, you and your doctor will have to talk about changing your HIV medicines.
Your doctor might also want you to have a PVL test if you get another infection or if your CD4 cell count goes down.
It is usually best not to get a PVL test for 3 to 4 weeks after you have an immunization shot or for 1 month after you have an infection. Your PVL could be higher than usual at these times.
How do HIV medicines affect the PVL?
After you start taking HIV medicines or change to different medicines, your PVL should decrease significantly in the first 1 to 2 months. This means the medicine is working. Your PVL should continue to decrease after that. If the medicines continue to work, your PVL can get so low that after 4 to 6 months of treatment it will be almost impossible to detect the HIV virus in your body. An undetectable level is good, but it does not mean that you are cured or that HIV is completely out of your body. It is important to note that not everyone's PVL gets this low.
How fast your PVL goes down depends on many things, including the following:
- How high it was to begin with
- How carefully you are taking your medicines
- Whether you were taking other HIV medicines previously
Special tests show that even people who have undetectable levels of HIV still have very small amounts of the virus in their blood. So even if your HIV level is undetectable, you need to get a PVL test several times a year. And it's important to remember that you could still infect other people if you have unsafe sex or if you share a needle.
Plasma Viral Load Testing in the Management of HIV Infection by E Mylonakis, M.D., M Paliou, M.D., and JD Rich, M.D., M.P.H. (American Family Physician February 01, 2001, http://www.aafp.org/afp/20010201/483.html)
Written by familydoctor.org editorial staff