Also Known As
Anti-retroviral Drug Resistance Testing
ARV Resistance Testing
genotypic resistance assay (GRA)
Formal Name
Human Immunodeficiency Virus Genotypic Resistance Testing
This article was last reviewed on
This article waslast modified on 25 July 2023.
At a Glance
Why Get Tested?

If you have been diagnosed with HIV, this test can be used to help doctors select the right drugs for treating the infection.

When To Get Tested?

Before starting HIV treatment (anti-retroviral therapy), or if your HIV viral load increases (or does not decrease) even though you are receiving anti-retroviral therapy

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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 anti-retroviral therapy or ART.

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.

Accordion Title
Common Questions
  • 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?

    Genotypic resistance testing is used by specialist doctors who treat patients with HIV and is only available at specialist laboratories.