Glossary of Terms

If you’re not familiar with HIV or if you or someone you know has just been diagnosed, you may come across some new terms that you’ve never seen before.

Below we’ve share some basic definitions (courtesy of NAM aidsmap) that cover some of the basic terms to get you started.

HIV

Human immunodeficiency virus, the virus which causes AIDS. There are two variants: HIV-1, and HIV-2. HIV-1 is by far the most common worldwide. See ‘subtype’ for more information.

AIDS

Acquired Immune Deficiency Syndrome. A collection of specific illnesses and conditions which occur because the body’s immune system has been damaged by HIV.

Antiretroviral (ARV)

A substance that acts against retroviruses such as HIV. There are several classes of antiretrovirals, which are defined by what step of viral replication they target: nucleoside reverse transcriptase inhibitors; non-nucleoside reverse transcriptase inhibitors; protease inhibitors; entry inhibitors; integrase (strand transfer) inhibitors.

CD4 cell count

A test that measures the number of CD4 cells in the blood, thus reflecting the state of the immune system. The CD4 cell count of a person who does not have HIV can be anything between 500 and 1500. When the CD4 count of an adult falls below 200, there is a high risk of opportunistic infections and serious illnesses.

Combination therapy

A therapy composed of several drugs available either as separate tablets, or as fixed-dose combination (FDC).

Confirmatory test

A second test, to show that the result of a previous test was correct. Because the diagnosis of HIV infection is so important, a second (confirmatory) test, is done. The confirmatory test should be of a different type than the first test.

Detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.

Immunosuppression

A reduction in the ability of the immune system to fight infections or tumours.

Post-exposure prophylaxis (PEP)

A month-long course of antiretroviral medicines taken after exposure or possible exposure to HIV, to reduce the risk of acquiring HIV.

Pre-exposure prophylaxis (PrEP)

Antiretroviral drugs used by a person who does not have HIV to be taken before possible exposure to HIV in order to reduce the risk of acquiring HIV infection. PrEP may either be taken daily or according to an ‘event based’ or ‘on demand’ regimen.

Undetectable = Untransmittable (U=U)

U=U stands for Undetectable = Untransmittable. It means that when a person living with HIV is on regular treatment that lowers the amount of virus in their body to undetectable levels, there is zero risk of passing on HIV to their partners. The low level of virus is described as an undetectable viral load. 

Undetectable viral load

A level of viral load that is too low to be picked up by the particular viral load test being used or below an agreed threshold (such as 50 copies/ml or 200 copies/ml). An undetectable viral load is the first goal of antiretroviral therapy.

For a full A to Z of HIV-related words and phrases visit the NAM aidsmap website.

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