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Am Fam Physician. 2001;63(3):495-496

What is a plasma viral load test?

A plasma viral load test (also called a PVL test) measures how much HIV is in your blood. The amount of virus in your blood is called your viral load. HIV means “human immunodeficiency virus.”

If your doctor knows your viral load, he or she can tell more about your risk for health problems caused by HIV infection. A PVL test helps 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 are used:

  • The polymerase chain reaction (PCR) test

  • The branched-chain DNA (bDNA) test

  • The nucleic acid sequence-based amplification (NASBA) test

All of these tests work well. Each of them can give a little different number for the amount of HIV in your blood. It is good to use the same test all the time.

Changes in PVL are often called log changes. For example, if your PVL test shows that you have 20,000 HIV copies per mL of plasma, a log change would be a 10-times change from your previous test (either an increase to 200,000 copies per mL or a decrease to 2,000 copies per mL).

The amount of HIV in your blood may change. That is why decisions about your HIV medicines are usually made after your doctor has checked two PVL tests done 2 to 3 weeks apart.

How does a PVL test help me decide when to start taking HIV medicines?

If you have not started taking medicines for HIV infection, your doctor will usually want to test your PVL several times a year to see if the amount of HIV in your blood is changing.

You might think about starting to take HIV medicines if your PVL is higher than 10,000 to 30,000 copies per mL. This is a complicated decision to make. It means you have to think about the other medicines you are taking and the other health problems you have. A PVL test result may lead to different decisions for every person.

Another measurement that can be taken with the PVL test is the CD4+ cell count. 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.

How are PVL tests used during HIV treatment?

If you are already taking medicines to treat HIV infection, your doctor will want you to get a PVL test several times a year to make sure that the medicines keep working for you.

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

What do HIV medicines do to the PVL?

After you start taking HIV medicines or change to different medicines, your PVL should go down at least one log (10 times) in the first one to two months. Your PVL should keep going down after that. If the medicines are working for you, after four to six months your PVL will get so low it will be almost impossible to detect.

How fast your PVL goes down depends on many things:

  • How high it was to begin with

  • How carefully you are taking your medicines

  • Whether you were taking other HIV medicines before

Not everyone is able to get down to an undetectable amount of HIV in the blood. An undetectable level is good, but it does not mean that you are cured or that HIV is completely out of your body. There is no cure for HIV infection, but keeping a low PVL level helps you feel well.

Special tests show that even people with 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 PVL tests several times a year. You could still infect other people if you have unsafe sex (sex without a condom) or if you share a needle.

If your PVL goes up, you and your doctor will have to talk about changing your HIV medicines.

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Copyright © 2001 by the American Academy of Family Physicians.

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