Who Should Get a Resistance Test?

Part of A Guide to HIV Drug Resistance

People Who Have Never Taken HIV Medications

In people who are infected with drug-resistant HIV, the majority of the HIV in their bodies will be mutated. One or more of these mutations will prevent HIV meds from working as well as they should.
In people who are infected with drug-resistant HIV, the majority of the HIV in their bodies will be mutated. One or more of these mutations will prevent HIV meds from working as well as they should.

How is it possible to be resistant to HIV medications before you've even taken them? Unfortunately, it's easier than you might think. In the United States, an average of 7% to 19% of newly infected people have mutations that are associated with drug resistance to at least one drug -- and, in some cases, to a whole class of medications.

How does this happen? The person you got HIV from may have been on HIV treatment, and his or her virus became resistant to one or more medications. Transmitted along with HIV was their resistance to certain drugs. If you were infected within the last several years, taking a resistance test before beginning HIV treatment will reveal whether you have HIV that is resistant to any HIV medications.

However, if you were infected more than a few years ago, or if you are not sure when you were infected, current resistance tests may not be able to provide a completely accurate result. This is because, after a few years, without HIV treatment, wild-type HIV will reproduce more than the drug-resistant virus you were originally infected with, and that wild-type HIV will once again become the most common type of HIV in your body.

Currently available resistance tests are not sensitive enough to detect mutations when they are present in small numbers in your body; they are most likely still there, but in low numbers.

So, for example, if you got HIV from a person who had resistance to Sustiva (this drug is one of the three drugs in Atripla), and a few years went by before you started taking HIV medications, a resistance test may not note that you have any mutations to Sustiva. But if you then start to take Sustiva, the Sustiva-resistant virus in your body will once again thrive.

While these tests may not detect resistance in people who were infected several years ago, it's still best to get one as soon as possible after you're diagnosed. If the test does find resistance, this information will be extremely helpful when it comes time to choose your first treatment regimen.

People Whose Viral Load Rises While on Treatment

If you're currently receiving HIV treatment and your viral load rises sharply, this could indicate that you're experiencing what your doctor might call "treatment failure." Although it sounds worse than it actually is, it could mean that your HIV has grown resistant to one or more of the medications you're taking.

However, a rising viral load can signify other things as well. Your body could be reacting to a recent vaccination or an infection. Or, a new HIV drug you just started taking could be interacting with other drugs you're taking, making your treatment less powerful.

Once your doctor rules out all these other possibilities, and before you stop or change treatment, it's critical to immediately get a resistance test. This way you can learn which drug is failing to keep your HIV under control and switch medications if necessary.

Quick timing is essential because once you stop or change medications, your drug-resistant HIV may become harder to detect, since many mutations thrive only when you're taking the medication they're resistant to. When not taking medications, wild-type HIV will become the most numerous type of HIV in your body and mutated HIV will be more difficult to measure.

People Who Need to Change Medications Due to Side Effects

Let's say you've been on HIV medications and, due to side effects, you need to change one or more drugs. If your viral load is above 1,000 copies, you should get a resistance test. Once again, make sure you get the test before you stop or change treatment. The test may help you be sure that a new medication will work at its full power.

If you have a viral load below 1,000 at the time you decide to switch medications, though, a resistance test might not be ordered because even though drug resistance mutations may be present, they are more difficult to reliably find when someone's viral load drops below 1,000.

Pregnant Women

To avoid passing HIV to their babies, it's best for pregnant women with HIV to make sure they have an undetectable viral load. If you're pregnant and getting HIV treatment but you have a detectable viral load, resistance testing may help figure out which drugs aren't working and which will have the best chance of preventing your baby from getting HIV.

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