HIV and Plasma Viral Load Testing

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."

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 you and your doctor decide if it is time for you to start taking medicines for HIV or to change to different medicines.

Three different PVL tests can be used:

All of these tests work well. Each test gives a different measurement for the amount of HIV in your blood. It is important to use the same test each time to be able to compare the results.

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 indicated for 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.

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 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.

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.

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. 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.

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 or for 1 month after you have an infection. Your PVL could be higher than usual at these times.

After you start taking HIV medicines or change to different medicines, your PVL should go down at least 1 log (10 times) in the first 1 to 2 months. Your PVL should keep going down after that. If the medicines are working for you, your PVL will get so low after 4 to 6 months that it will be almost impossible to detect. An undetectable level is good, but it does not mean that you are cured or that HIV is completely out of your body. Not everyone's PVL gets this low.

How fast your PVL goes down depends on many things, including the following:

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 (sex without a condom) or if you share a needle.