HIV genotype testing: Preparation, Procedure and Test Result

HIV 1 Genotyping identifies mutations in HIV 1 Reverse Transcriptase & Protease genes.

June 2, 2018

HIV genotype testing: Preparation, Procedure and Test Result

Mutations in HIV happens as a result of high replication rate of HIV 1 coupled with its rapid mutation rate which reduce susceptibility to antiretroviral agents.
HIV 1 Genotyping identifies mutations in HIV 1 Reverse Transcriptase & Protease genes. It also helps in identifying the mutations associated with resistance so that Anti HIV 1 treatment regimens can be altered.

Preparation for HIV genotype testing:

No special preparation required for this test. A blood sample will be drawn from a vein in your arm for this purpose.

Purpose of HIV genotype testing:

If you have been diagnosed with human immunodeficiency virus (HIV), this test is done to determine whether the strain causing your infection is resistant or has developed resistance to one or more antiretroviral therapy (ART) drugs.
This will help your doctor determine the proper treatment regimens. If it is found to be resistance with some antiretroviral therapy (ART) drug, others can be used.
This test should be done when you are first diagnosed with HIV, immediately prior to the start of antiretroviral therapy, or when you are receiving ART but the HIV viral load does not decrease or rises steadily.
Generally, a treatment is considered a failure if a viral load rises more than three fold in consecutive tests. If drug resistance is found, a new treatment regimen may be chosen.
Human immunodeficiency virus (HIV) genotypic antiretroviral drug resistance testing evaluates weather the HIV strain infecting an individual is resistant or has developed resistance to one or more antiretroviral therapy (ART) drugs.
The genes of the HIV strain infecting the person can be analyzed in this test to identify mutations that may cause the virus to be resistant to ART. Someone may be initially infected with a drug resistant HIV strain or drug resistance may develop during treatment.
Drug resistance is a condition in which a microorganism is able to survive, grow and/or multiply in the presence of one or more antimicrobial drugs as the drug is not responding. when antimicrobials are used to treat an infection and a mutation or change occurs in one of the genes of the microorganism, resistance can develop.
This change leads to a mixed population in the body of infected person containing some microorganisms that are drug-resistant and some that are drug-sensitive. Microorganisms without the mutation are killed by the drug as they are drug sensitive, but those that have the mutation quickly multiply and begin to predominate. This condition is called selective pressure because the drug selects and allows the proliferation of the genetic forms of the microorganism that are resistant to it. When this occurs, the antimicrobial is no longer effective in treating the infection.
Even in the absence of drug treatment, HIV can mutates. However, not necessarily every mutation causes resistance to antiretroviral drugs. The genetic code of the HIV a person has been infected with is analyzed in genotypic resistance testing to determine if there are any genetic mutations that are known to cause ART resistance.  
Testing is used to identify resistance to antiretroviral drugs in classes such as:

  • Protease inhibitors
  • Reverse transcriptase inhibitors
  • Integrase inhibitors

Often individuals with HIV are recommended to be treated with a combination of drugs that are from two different classes of antiretroviral drugs to avoid the development of ART resistance. This is known as highly active antiretroviral therapy or HAART.

Test Result:

The test can detect the the mutations which indicate the drugs to which the HIV strain is likely to be resistant. However, not necessarily all mutations cause drug resistance and therefore, the results of genotypic resistance testing must be interpreted with caution. A specialist may be consulted when considering results of the test and selecting appropriate ART.
The test results identify the viral mutations detected. These are described by a combination of letters and numbers where the letters refer to the amino acid associated with the gene and the number refers to the position of the mutation in the genome. for example, K103N.
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 doctor to select a treatment regimen that will be be effective in suppressing the HIV in patient.
If the viral load of a person is less than 500 copies/mL, this test is not recommended. This is because there is insufficient amount of HIV genetic material (RNA) for testing to be reliable. Test results can be reliable if the viral load is greater than 1,000 copies/mL. However, testing is recommended even if the level is between 500 and 1,000 copies/mL.
HIV genotypic resistance is a qualitative test and detects mutations associated with drug resistance and not the level of resistance associated with the drug. Phenotypic resistance testing is a better indicator of the level of HIV drug resistance.
The unknown resistance mutations that may be present in rare strains of HIV can not be detected by HIV genotypic resistance testing. Also, the test may not detect a drug resistant strain of HIV if the resistant gene is only present in less than 10 to 20 percent of total virus that is circulating in the blood.
As the percentage of drug resistant strain may decrease considerably in the absence of the drug, testing is not recommended after discontinuing a drug. When selective pressure from a drug is absent, testing would not be able to detect it as the drug resistant strain may have drop drastically. Therefore, testing should be done while a person is taking the drugs, or if this is not possible, then within 4 weeks of stopping therapy to evaluate a failed treatment.
Results may take one to two weeks to get ready.