HIV Genotypic Resistance

By Fisher, Steve 
December 26, 2017

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?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be 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. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 


December 26, 2017


Ferri F. Ferri's Clinical Advisor. 2016, pp. 639-45.e1., Human Immunodeficiency Virus. Ferri’s Clinical Advisor. Ferri FF. 2016, pp. 639-45., Mandell G. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 2009, 7th ed., McPherson. Henry's Clinical Diagnosis and Management by Laboratory Methods. 2017, 23rd ed., pp. 1093-97., Overview of HIV drug resistance testing assays. UpToDate.

Reviewed By:  

Fraser, Marianne, MSN, RN,Haldeman-Englert, Chad, MD