HIV Resistance Testing
A blood sample taken from a vein in your arm
In HIV resistance testing, the genes of the HIV virus are examined to look for changes that may stop anti-retroviral drugs from working. Changes (mutations) in the genetic code of the HIV virus happen by chance when new copies of the virus are made. These mutations can sometimes alter the virus so that it is no longer affected by an anti-retroviral drug and can keep multiplying. This is known as drug resistance.
During an HIV resistance test, the genetic code of the HIV virus in your blood is checked to see if there any mutations that are known to cause drug resistance. For certain drugs, even single mutations of a gene can cause resistance. For other drugs, several mutations tend to combine to cause resistance.
A strain of virus that is resistant to a drug will multiply and become the most common form of the virus in the body (as all the other forms are destroyed by the drug). To avoid the development of antiviral drug resistance, it is usually recommended that you be treated with a combination of drugs that are from two different classes of antiretroviral drugs. This is known as highly active anti-retroviral therapy or HAART.
How is the sample collected for testing?
A sample of blood is taken from a needle placed in a vein in your arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Genotypic resistance testing helps doctors make better treatment decisions when starting therapy and when existing anti-retroviral therapies are not working effectively. If drug resistance is found, a new treatment regimen may be chosen.
When is it requested?
Genotypic resistance testing is requested on first diagnosis; when starting anti-retroviral therapy; and if the amount of HIV in your blood rises steadily (or does not fall) despite therapy, indicating the possibility of resistance.
What does the test result mean?
The test result identifies the genetic mutations in the HIV virus. These are described by a combination of letters and numbers, for example K103N. Not all mutations cause drug resistance. Based on the test result, your doctor will identify whether your HIV virus population has any mutations causing drug resistance.
Is there anything else I should know?
Genotypic resistance testing is used by HIV specialist doctors as a normal part of HIV treatment. The test is not good at detecting 'minority' mutations, which are those affecting less than 20% of the virus population.
Genotypic resistance testing works best on blood samples with a viral load of at least 1,000 copies per millilitre of blood. If your viral load is very low, the test probably won’t work. If your viral load is undetectable, genotypic resistance testing cannot be performed.
Is genotypic resistance testing widely available?
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Conditions: Human Immunodeficiency Virus (HIV), Sexually Transmitted Diseases
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