What is a viral load?

An HIV viral load is the amount of HIV measured in a volume of blood. The goal of HIV treatment is to lower viral load to be undetectable. That is, the goal is to reduce the amount of HIV in the blood enough so that it can’t be detected in a laboratory test.

For people living with HIV, it can be helpful to know their own HIV viral load because it tells them how well their HIV medication (antiretroviral therapy) is working. Read on to learn more about HIV viral load and what the numbers mean.

HIV attacks CD4 cells (T-cells). These are white blood cells, and they’re part of the immune system. A CD4 count provides a rough assessment of how healthy a person’s immune system is. People who don’t have HIV usually have a CD4 cell count between 500 and 1,500.

A high viral load can lead to a low CD4 cell count. When CD4 count is below 200, the risk of developing an illness or infection is higher. This is because having a low CD4 cell count makes it harder for the body to fight infection, increasing the risk of illnesses such as severe infections and some cancers.

Untreated HIV can cause other long-term complications and can develop into AIDS. However, when HIV medication is taken daily as prescribed, the CD4 count tends to increase over time. The immune system gets stronger and better able to fight infections.

Measuring viral load and CD4 count shows how well HIV treatment is working both to kill the HIV in the bloodstream and to allow the immune system to recover. The ideal results are to have an undetectable viral load and high CD4 count.

Viral load testing shows how much HIV is in 1 milliliter of blood. A viral load test is done at the time someone is diagnosed with HIV before treatment is started, and again from time to time to confirm that their HIV treatment is working.

Raising CD4 count and lowering viral load requires taking medication regularly and as instructed. But even if a person takes their medication as prescribed, other prescription and over-the-counter (OTC) medications, recreational drugs, and herbal supplements they use can sometimes interfere with the effectiveness of HIV treatment. It’s always a good idea to check with a doctor before starting any new medications, including OTC and prescription drugs and supplements.

If testing shows that a person’s viral load hasn’t become undetectable or that it’s gone from being undetectable to detectable, their doctor may adjust their antiretroviral therapy regimen to make it more effective.

The higher the viral load, the higher the probability of passing HIV on to someone else. This could mean passing the virus to a partner through sex without a condom, to someone through sharing needles, or to a baby during pregnancy, delivery, or breastfeeding.

When taken consistently and correctly, antiretroviral medication decreases viral load. This decreased viral load reduces the risk of passing HIV on to someone else. Alternatively, not taking this medication consistently or at all increases the risk of passing HIV to someone else.

Having an undetectable viral load doesn’t mean a person’s cured, because HIV can still hide in other parts of the immune system. Rather, it means the medication they’re taking is effective at suppressing the growth of the virus. Ongoing suppression can only be achieved by continuing to take this medication.

Those who stop taking the medication risk having their viral load go back up. And if viral load becomes detectable, the virus can be passed to others through bodily fluids such as semen, vaginal secretions, blood, and breast milk.

Sexual transmission

Having an undetectable viral load means that the risk of passing HIV to someone else is effectively zero, assuming that the person with HIV and their partner don’t have any sexually transmitted infections (STIs).

Two 2016 studies, in the Journal of the American Medical Association and The New England Journal of Medicine, found no transmission of the virus from an HIV-positive partner who had been on antiretroviral therapy for at least six months to an HIV-negative partner during sex without condoms.

However, researchers are unsure about the effects of STIs on risk of HIV transmission in treated individuals. Having an STI might increase the risk of transmitting HIV to others even if HIV isn’t detectable.

Transmission during pregnancy or breastfeeding

For women who are pregnant and living with HIV, taking antiretroviral medication during pregnancy and labor dramatically reduces the risk of transmitting HIV to the baby. Many women living with HIV are able to have healthy, HIV-negative babies by accessing good prenatal care, which includes support for antiretroviral therapy.

Babies born to HIV-positive mothers receive HIV medication for four to six weeks after birth and are tested for the virus over the first six months of life.

According to the Centers for Disease Control and Prevention (CDC), a mother with HIV should avoid breastfeeding.

It’s important to track viral load over time. Any time viral load increases, it’s a good idea to find out why. An increase in viral load can occur for many reasons, such as:

  • not taking antiretroviral medication consistently
  • the HIV has mutated (changed genetically)
  • antiretroviral medication isn’t the right dose
  • a lab error occurred
  • having a concurrent illness

If viral load increases after being undetectable while on treatment with antiretroviral therapy, or if it doesn’t become undetectable despite treatment, the healthcare provider will likely order additional testing to determine the reason.

The frequency of viral load testing varies. Typically, viral load testing is done at the time of a new HIV diagnosis and then intermittently over time to confirm that antiretroviral therapy is working.

A viral load usually becomes undetectable within three months of starting treatment, but it often happens faster than that. A viral load is often checked every three to six months, but it may be checked more often if there is concern that the viral load may be detectable.

Whatever their viral load, it’s a good idea for people living with HIV to take steps to protect themselves and their sexual partners. These steps may include:

  • Taking antiretroviral medication regularly and as directed. When taken properly, antiretroviral medication reduces viral load, thus decreasing the risk of transmitting HIV to others. Once viral load has become undetectable, the risk of transmission through sex is effectively zero.
  • Getting tested for STIs. Given the potential effect of STIs on risk of HIV transmission in treated individuals, people with HIV and their partners should be tested and treated for STIs.
  • Using condoms during sex. Using condoms and engaging in sexual activities that don’t involve exchange of bodily fluids lowers risk of transmission.
  • Considering PrEP. Partners should to talk to their healthcare provider about pre-exposure prophylaxis, or PrEP. This medication is designed to prevent people from getting HIV. When taken as prescribed, it decreases the risk of acquiring HIV through sex by more than 90 percent.
  • Considering PEP. Partners who suspect that they’ve already been exposed to HIV should to talk to their healthcare provider about post-exposure prophylaxis (PEP). This medication reduces the risk of infection when it’s taken within three days after possible exposure to HIV and continued for four weeks.
  • Getting tested regularly. Sexual partners who are HIV-negative should get tested for the virus at least once a year.

An HIV diagnosis can be life-changing, but it’s still possible to be healthy and active. Early diagnosis and treatment can reduce viral load and risk of illness. Any concerns or new symptoms should be brought to a healthcare provider’s attention, and steps should be taken to live a healthy life, such as:

  • getting regular checkups
  • taking medication
  • exercising regularly
  • eating a healthy diet

A trusted friend or relative can provide emotional support. As well, many local support groups are available for people living with HIV and their loved ones. Hotlines for HIV and AIDS groups by state can be found at ProjectInform.org.

Read this article in Spanish.