Viral load is the amount of HIV in your bloodstream. It is measured using one of two techniques; a polymerase chain reaction (PCR test), or a branched DNA (bDNA test).

Viral load tests are an important tool to:

• Monitor HIV progression
  While CD4 cell counts are your best measurement of how healthy your immune system is today, viral load tests can help figure out whether you’re at risk for more immune damage in the near future. When compared over time, viral load results tell you whether the amount of HIV in your bloodstream is higher or lower than it was before. The higher your viral load, the more likely you are to lose CD4 cells in the future.
• Figure out when it’s time to start treatment
  CD4 cell counts and viral load levels are used together to determine when you may need treatment. You should also consider how you feel, what is going on in your life, and which treatments you will or won’t take or be able to access. The U.S.-based Department of Health and Human Services (DHHS) Guidelines committee makes recommendations on how best to use anti-HIV drugs. The Guidelines state that people with higher viral loads (above 55,000) may be at greater risk for HIV-related complications and should consider starting treatment. Women with HIV may be at risk for developing complications at viral loads slightly lower than 55,000.
• Measure how well HIV drugs are working
  HIV drugs work by preventing the virus from reproducing. When a regimen is working, the viral load usually goes down within weeks of starting. If viral load goes up while using HIV drugs, you and your doctor should take another viral load measurement, and look closer to see if there are any problems with adherence or resistance, and determine whether you may need to change drugs in your regimen. 

One goal of HIV treatment is to keep viral load levels as low as possible for as long as possible. With effective HIV treatment regimens, viral load can be reduced to levels that cannot be detected by lab tests. With most viral load tests this is below 50 copies per mL of blood.

Even if your viral load is undetectable, HIV is still in your body in very small quantities, in places like the lymph nodes, spleen, and genital tract. If you stop taking your HIV drugs, the virus usually starts multiplying and eventually, the viral load increases.

You and your doctor should determine the schedule that works best for you. In general, you should have a viral load test when you are first diagnosed and every three to six months when you are not on HIV therapy.

Consider having a viral load test before starting treatment and another test two to eight weeks later. If the regimen is working to suppress HIV reproduction, your viral load should drop by 90% within two months and be undetectable within six months of starting treatment. Once viral load goes to undetectable, viral load is usually measured every 3 to 6 months.

If these levels are not achieved after starting treatment, or if your viral load has recently become detectable on stable therapy and keeps increasing, it can signal that your regimen isn’t controlling HIV as well as it should. You and your doctor should consider all possible reasons (problems with drug absorption, adherence, or drug resistance) and take steps to correct the problem, including additional testing and considering changing drug treatments.

Background on viral load testing:

Our understanding of viral load has grown enormously since 1996, when the first test was approved and began to be widely used. Most early clinical trials that studied the role of viral load looked primarily at groups of men. Women were not enrolled in enough numbers in these trials for anyone to know whether there were sex-based differences in viral load. Similarly, when the first reports that women had lower baseline viral load appeared in 1996, it wasn’t clear whether this was true of all women, or just the women being studied.

Since 1996, more than 15 studies have compared viral load levels between groups of men and women. A majority of these studies found sex differences in viral load, even when things like CD4 count, time of infection, age, race, HIV drug use, and other factors were similar. At similar CD4 cell counts, women tend to have consistently lower viral load levels than men, by as much as 50 to 85 percent. The differences seem greatest during the early course of HIV infection. In more advanced stages of HIV, when people have CD4 cell counts less than 350, the difference between viral load levels in men and women appears to get smaller or go away.

In men, studies found that initial viral load predicts risk of progression to AIDS. If the same were true for women, then lower viral loads would mean lower risk for disease progression. However, several large reliable studies have shown that women progress to AIDS at similar rates to men even with lower viral loads early on. So, initial viral load may not have the same ability to predict disease progression in women as it does in men.

Women seem to have different absolute viral load values than men. In other words, even though viral load levels can predict a woman’s risk for immune damage, women may develop AIDS at lower viral load levels than men with similar CD4 counts. The current DHHS Guidelines about when to start treatment are based on viral load and CD4 counts. The Guidelines are always changing, but currently suggest that anyone with CD4 cell counts below 350, or viral load above 55,000, should consider treatment.

In 2002, in response to community advocacy, a discussion of differences in viral load was added as a supplement to the DHHS Guidelines. The supplement reviews the evidence about sex differences in viral load, emphasizing that differences occur when CD4 counts are high, at a time when treatments are recommended based on viral load levels. The supplement states that since women tend to have lower absolute viral load values, clinicians may want to consider treating their female patients with CD4 cells above 350 before their viral loads reach 55,000.

Many clinicians feel that CD4 cells are a better indicator of when it’s time to start therapy in women. If you are thinking about starting treatment, it is important to take into account your viral load, CD4 cell count, other labs results, and how you are feeling. Talk to your doctor about the best treatment plan for you.

Researchers have increasingly used measurements of genital viral load as well as blood viral load to learn more about how reproductive hormones, contraceptives, and immune cells influence viral loads in women. It has been noted that viral load and the level of certain HIV drugs fluctuate throughout the course of a single menstrual cycle. This could have an impact on drug dosing and timing of viral load tests in women. More research is needed to determine if women should start treatment earlier than men, and if so, at what viral load level. Understanding more about sex differences in viral load will lead to better care for HIV+ women.

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