HIV Specific Laboratory Tests

Reviewed by: HU Medical Review Board | Last reviewed: September 2019

Although an individual with HIV may need to undergo many laboratory tests to help guide their treatment and get more information on their health status, there are several tests that are specific to HIV. Several of these, and their general frequency, are below. However, your doctor or healthcare provider will know your specific situation best, and will determine the most appropriate testing schedule for you. It’s always important to follow your healthcare provider’s instructions for the timing of lab tests, as they may impact your HIV treatment.

What is a CD4 count?

CD4 cells, also called T-cells, are cells that are part of the immune system and help our bodies fight off infections and other foreign invaders. A normal CD4 count in a healthy individual can be anywhere from 500-1,500 cells/microliter. When an individual has late-stage HIV, also called AIDS (acquired immunodeficiency syndrome), their CD4 count is below 200 cells/microliter (also referred to as a CD4 count of 200) and/or they have one of the many AIDS-defining illnesses. An individual’s CD4 count can predict how active their HIV is and their overall prognosis.1-3

Why are CD4 cells important?

Without CD4 cells, we are much more susceptible to illnesses, foreign invaders, and cancers. One thing that is of particular importance for individuals with low CD4 counts is opportunistic infections. An opportunistic infection is one that normally wouldn’t affect an individual with a healthy immune system, but can greatly affect someone with HIV. We are exposed to possibly infectious agents every day; however, our bodies are able to fight them off. If our immune system is damaged by HIV, we are unable to fight off these common invaders like we used to. These infections can take over our bodies and be potentially life-threatening. This is why monitoring CD4 count is so important in HIV care.

Monitoring CD4 count

An HIV-positive individual’s CD4 count is typically first measured when they are diagnosed or start with a new healthcare provider. If they start antiretroviral therapy (ART, medications used to suppress the virus), their CD4 count will be measured when they begin treatment.

An individual’s CD4 count can also be monitored throughout treatment to determine how well an ART regimen is working. During the first two years of an ART regimen, an individual’s CD4 count may be tested every three to six months. After two years on the same therapy, these tests may be spaced out to about once a year, if counts are consistently between 300 and 500, and even less frequently if counts are greater than 500 after two years on the same treatment. CD4 counts may have to be monitored more frequently if an individual’s viral load (how much active virus is in the body) is consistently high. If an ART regimen is changed, CD4 testing may be required. If an individual chooses not to start treatment, their CD4 count should be monitored every three to six months.2,4

What is an HIV viral load?

A viral load is a measure of how much HIV is in the body. It measures how many copies of HIV are found in one milliliter of blood. Well-controlled HIV is considered to be around 200 copies per milliliter or less. Someone without HIV will have zero copies of the virus per milliliter. Eventually, a person’s viral load can become “undetectable” meaning that the amount of HIV in the blood is so low, the virus is not detected when tested. This typically happens around 50 copies per milliliter or less. Controlling viral load is essential for those with HIV to lead a longer life with fewer HIV-related complications.2,4,5

Recent research has suggested that those who achieve and maintain, an undetectable viral load have virtually no risk of transmitting the virus to an HIV-negative partner. This idea has been referred to as “undetectable = untransmittable” or “U=U”. Therefore, the risk of HIV transmission to an HIV-negative partner can be reduced when an HIV-positive partner is on ART and taking their medications as prescribed.5-7

Monitoring viral load

Viral load is typically monitored more frequently than CD4 count, as it predicts how well an individual is responding to treatment. It is tested when a person starts with a new healthcare provider and again when starting ART (if not at the same time). After ART is started, a person’s viral load will be tested within two to four weeks. After the initial viral load test once treatment is started, viral load is generally measured every month to two months until it is considered suppressed (less than 200 copies per milliliter).

Once viral load is suppressed, monitoring can be extended to every three to four months for the first two years of treatment. After two years on the same treatment, if viral load is still suppressed, this can be extended to every six months. If viral load is not suppressed, monitoring may need to be more frequent in the longer-term. This pattern is repeated for any changes in ART, including starting a new ART regimen.2,4

What is HIV drug resistance testing?

Some strains of HIV may be resistant, or not respond to, common HIV medications. Additionally, HIV has the potential to mutate as it’s replicating inside the body and gain resistance to a medication that used to be able to treat it. Mutations can be prevented by starting treatment as soon as possible after diagnosis, and taking ART exactly as prescribed. When an individual is taking their ART as directed, it can suppress the virus greatly and prevent it from replicating. When HIV can’t replicate, it can’t mutate and gain resistance against drugs. When an individual skips doses or is not adherent to their medications, the amount of medication in their system will decrease, allowing HIV to replicate and mutate, and potentially, become resistant to the medication they’re taking.

Why is drug resistance testing important?

In order to determine if your HIV is resistant to certain medications, your healthcare provider will perform drug resistance testing. This testing is recommended before starting any ART in order to plan the best medication regimen possible. In some people, treatment may be started before the results of these tests come back, and adjusted later on, if need be. If an individual is already taking ART and is not achieving a reduction in viral load or has a high viral load while on therapy (such as over 1,000 copies of HIV per milliliter), drug resistance testing should be completed. If an individual has a moderately high viral load (such as between 500 and 1,000 copies per milliliter), drug resistance testing may be helpful, but is not required.2,4

Drug resistance tests look for mutations in HIV genes targeted by common ART medications, including genes called the protease, integrase, and reverse transcriptase genes.2,4 If your drug resistance tests come back positive, your healthcare provider will explain what mutations have occurred and how this will impact your treatment options moving forward.

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