If you have been diagnosed with human immunodeficiency virus (HIV), to determine whether the strain causing your infection is resistant or has developed resistance to one or more antiretroviral therapy (ART) drugs
HIV Drug Resistance Testing, Genotype
HIV Drug Resistance Testing, Genotype
Also Known As
Antiretroviral Drug Resistance Testing
ARV Resistance Testing
Formal Name
Human Immunodeficiency Virus Antiretroviral Drug Genotypic Resistance Testing
This article was last reviewed
on
This article waslast modified
on December 15, 2020.
At a Glance
Why Get Tested?
When To Get Tested?
When first diagnosed with HIV, immediately prior to the start of antiretroviral therapy, or when you are receiving ART but the amount of virus in your blood (HIV viral load) does not decrease or rises steadily
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is the test used?
HIV genotypic antiretroviral resistance testing is used to help select a drug regimen that will likely be effective in treating your HIV infection. The test is used to determine whether the HIV strain infecting you is resistant or has developed resistance to one or more drugs used to treat HIV. Testing analyzes the genes of the virus to detect the presence of one or more mutations that are associated with antiretroviral drug (ART) resistance.
- When you are first diagnosed, HIV drug resistance testing is used to determine whether the HIV strain is already resistant to one or more drugs. The information is used to identify and select the antiretroviral drugs that will likely be effective.
- Testing may also be used after you begin treatment to help determine the cause of drug treatment failure. Treatment failure is identified when your HIV viral load does not decrease or begins to increase despite treatment. In this case, your treatment will likely be changed. Results of antiretroviral resistance testing may help select a different drug regimen that may be effective in suppressing the virus.
Testing is used to identify resistance to antiretroviral drugs in classes such as:
- Protease inhibitors
- Reverse transcriptase inhibitors
- Integrase inhibitors
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When is it ordered?
HIV genotypic resistance testing is recommended when you are first diagnosed with an HIV infection and before starting therapy. If treatment is not started soon after diagnosis, then it is recommended that resistance testing be repeated before starting therapy.
Testing may also be ordered when your HIV viral load values do not decrease or they rise steadily during therapy, indicating that your HIV may be developing resistance. Generally, your treatment is considered a failure if your viral load rises more than three-fold in consecutive tests.
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What does the test result mean?
In general, the mutations detected by the test indicate the drugs to which the HIV strain is likely to be resistant. However, not all mutations cause drug resistance and the results of genotypic resistance testing must be interpreted with caution. A specialist may be consulted when considering results of your test and selecting appropriate ART.
The test results identify the HIV viral mutations detected. These are described by a combination of letters and numbers where the letters refer to the amino acid associated with the HIV gene and the number refers to the position of the mutation in the HIV's genome. For example, the mutation K103N may be detected. K is the amino acid and 103 is the position of the mutation.
The laboratory report may also provide an interpretation and a list of the drugs to which the virus is either resistant or susceptible. This information helps a healthcare practitioner select a treatment regimen that is likely to be effective in suppressing your HIV. If you are being treated with ART and the test results indicate that the HIV strain has become resistant to it, you will likely be switched to a new treatment regimen.
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How long will it take to get the results of my test?
Depending on where you have your test done, your sample may be sent to a reference laboratory. Results may take one to two weeks.
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What is HIV phenotypic resistance testing?
HIV phenotypic resistance testing is the same as genotypic testing in that it tests the strain of HIV causing your infection for resistance to specific ART, but it uses a different method. In the lab, a sample of the virus grown in culture is mixed with different concentrations of one or more drugs. If the virus is able to replicate in the presence of the drug, as compared to a known strain of virus (a reference virus), it is said to be resistant to that drug. This type of testing usually takes longer than genotypic resistance testing.
HIV genotypic resistance detects mutations associated with drug resistance. It does not report the level of resistance associated with the drug. Phenotypic resistance testing is a better indicator of the level of HIV drug resistance than genotypic testing.
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My healthcare practitioner says my viral load is too low for drug resistance testing. Why?
HIV drug resistance testing is not recommended if your viral load is less than 500 copies/mL. In this case, there is insufficient amount of HIV genetic material (RNA) for testing to be reliable. Testing works best if the viral load is greater than 1,000 copies/mL, but testing is recommended even if the level is between 500 and 1,000 copies/mL.
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Is there anything else I should know?
HIV genotypic resistance testing cannot detect unknown resistance mutations that may be present in rare strains of HIV. The test may not detect a drug-resistant strain of HIV if the resistant gene is only present in less than 10-20% of total virus that is circulating in the blood.
Testing is not recommended after discontinuing a drug. This is because the percentage of drug-resistant strain may decrease considerably in the absence of the drug. When "selective pressure" from a drug is absent, the drug-resistant strain may drop enough to the point where testing would not be able to detect it. Because of this, if testing is performed to evaluate a failed treatment, it should be done while a person is taking the drugs, or if this is not possible, then within 4 weeks of stopping therapy.
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An illustrative diagram of a single, infective viral particle of HIV virus. Image credit: National Institute of Allergies and Infectious Diseases (NIAID)