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HIV Genotypic Resistance

Does this test have other names?

Genotypic resistance assay

What is this test?

This blood test looks at the genetic makeup of a strain of HIV, the virus that causes AIDS.

If you are infected with HIV, this test may be done before you start taking antiviral medicine. It can help your healthcare provider figure out the best treatment to use. This helps because drug-resistant HIV strains continue to change.

The test can also help figure out if a medicine you are taking works for your type of HIV and whether your virus has mutated, or changed, in an effort to survive treatments. This test is only able to find known mutations.

Why do I need this test?

You may need this test if your healthcare provider suspects that the amount of HIV in your body is steadily increasing. This could happen even though you're taking antiviral medicines if you have a type of HIV that's resistant to treatment.

You may also have this test before starting HIV treatment. You might also be given this test if you are pregnant and need HIV medicines.

What other tests might I have along with this test?

Your healthcare provider may also do HIV phenotype resistance testing. But it takes longer to get the results for this test and the cost is higher. Also resistance measurements have not been set for all HIV medicines.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Test results include a combination of numbers and letters—for instance, K103N. Not all mutations of HIV resist drug treatment, but some are commonly found in HIV.

To get the best test results, you typically need to have at least 1,000 copies of the virus per milliliter of blood. The test may not be useful if you don't have enough copies of the virus in your blood.

This test may not find mutations that infect less than 20% of the virus population.  

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Not taking your HIV medicines as prescribed can cause what may look like an error in your results (false-positive).

How do I get ready for this test?

You don't need to prepare for this test.


Medical Reviewers:

  • Moloney Johns, Amanda, PA-C, MPAS, BBA
  • Snyder, Mandy, APRN