Why the HIV Viral Load Is Important

An undetectable viral load eliminate the risk of transmission

Lab technician holding vial of blood
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The HIV viral load is a measurement of the amount of HIV circulating in your blood if you are HIV-positive. The viral load is used to determine how effectively your antiretroviral drugs are working and can even tell doctors when your treatment is failing or you are not taking your drugs as prescribed.

Goals of Therapy

The goal of HIV therapy is to prevent HIV from replicating in order to bring the viral population down to an undetectable level. Undetectable does not mean that there is no virus or that the virus has suddenly been cleared from your body. It simply means that no virus can be detected using currently available testing technologies. Once ART is stopped, the virus will invariably return and start replicating again.

It is important to note that the HIV viral load can vary when testing blood and other body fluids. For example, an undetectable viral load in the blood doesn't necessarily mean that you are undetectable in semen. This phenomenon, known as viral shedding, can increase the risk of transmission from persons who might otherwise be considered virus-free.

People with uncontrolled viral loads risk severe damage to their immune system, the injury of which leaves the body exposed to an ever-increasing array of opportunistic infections.

How Testing Is Performed

Typically, your doctor will draw once every three to six months to measure your viral load. Newer, ultra-sensitive quantitative viral load tests can detect viral activity as low as five copies/mL to well over 1,000,000 copies per milliliter (copies/mL.

By contrast, qualitative HIV viral load tests are simply used to confirm the presence of HIV and are commonly used to test infants and newborns born to HIV-positive mothers.

The test involves a simple blood draw requiring 6 mL of blood (roughly one and a quarter teaspoons). You do need to fast or avoid medications before the blood draw.

Interpreting the Results

The aim of viral load is simple: the fewer copies of HIV in your blood the better. When starting treatment, viral load tests provide the baseline measures by which later tests are compared.

Every tenfold drop in viral load is considered a one-log drop. For example, if the viral load drops from 50,000 copies/mL to 500 copies/mL, the patient is said to have a two-log drop in viral load.

Generally speaking, with current generation HIV drugs, one can expect to have an undetectable viral load in anywhere from two to nine months. While the speed by which suppression is achieved can vary, it tends to be slower in persons who have delayed treatment and sustained severe immune damage.

We measure this by a person's CD4 count which quantifies how many defensive CD4 T-cells are remaining in the blood. A person with a normal immune function can have anywhere from 500 to 1,500 cells/mL, while persons with a compromised immune system will have less than 200 cell/mL.

Moreover, if a person has developed or acquired resistance to any of the prescribed drugs, the likelihood of viral suppression may also be severely compromised. In such a case, treatment will need to be changed after genetic testing reveals which drug or drugs the patient is resistant to.

Benefits of Viral Suppression

The aim of HIV therapy is to sustain undetectable viral loads for many years which not only preserves future treatment options but reduces the risk of serious illness by 53 percent (according to a 2011 study in the New England Journal of Medicine).

Additionally, sustaining an undetectable viral significantly reduces your chance of passing the virus to others, a prevention strategy known as treatment as prevention (TasP).

Current research has shown that having and maintaining an undetectable viral load eliminates your risk of transmitting HIV to an uninfected partner, whether for anal, vaginal, and oral sex.

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