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Viral Load Testing -- What's the Story?

February 26, 1999

A viral load test measures the amount of HIV in your blood. The result of the test is called the "viral load."

The test is relatively new. It measures how much HIV is circulating in your blood. The higher the number of your viral load test, the more HIV there is in your blood.

The test result number is the number of HIV RNA copies in 1 ml. (about a quarter of a teaspoon) of your blood. RNA is part of HIV, and each HIV virus has two copies of RNA.

There are two types of viral load tests in common use. One is called a PCR test, and the other a bDNA test. Be sure that you're always getting the same kind of test, since the results of one test can't be directly compared to the other. Most tests today are PCR tests. PCR and bDNA tests differ in how well they can detect small amounts of virus.

What does "undetectable" mean?

People talk about their HIV being "undetectable." What that means depends on the particular test used and how well it can detect small amounts of HIV. Most PCR tests in use can't detect less than 400 copies of HIV RNA. So, if you really have 350 copies, this test will say you have "undetectable" HIV.

Other commercially available tests can detect as few as 20 copies, so with 350 your HIV would be detectable if this test were used.

You'll know which test was used because the results will tell you this information.

The viral load test isn't very precise. This means that the difference between two tests has to be pretty big for it to be meaningful. One test result has to differ from another by at least three times to be considered a real change.

For example: results of 200,000 and 400,000 aren't really different because 400,000 is only twice as big as 200,000. But results of 100,000 and 400,000 are meaningfully different because 400,000 is more than 3 times as large as 100,000.

Any infections, like the flu or bugs that cause diarrhea, can make your viral load go up significantly for a while. This can also happen after immunizations and, sometimes, after skin tests for TB.

So viral load tests taken while you have an infection or after immunizations may be unreliable. Wait 2-3 weeks after recovering from an infection or after immunizations to get a more reliable viral load result.

The viral load test is used for two purposes: to predict disease progression and to see how anti-HIV drugs are working.

1. Predicting HIV Progression

Studies show that, in general, higher viral loads predict a more rapid progression of HIV infection in most people. Usually, the viral load increases in untreated people. Higher viral loads only indicate a greater chance -- but not a certainty -- of more rapid disease progression.

What is a "high" viral load?

It depends on who you talk to. No one really knows, although there are lots of strong opinions. To some people, any detectable viral load is too high. The number may be over a million, which anyone would consider high. But whether 1000, 5000, 10,000 or 50,000 are high numbers that need to be brought down is a matter of opinion.

You may have to insist on a viral load test when you want it. Get the actual number (40,000, for example) and know which test was used. If your doctor is vague, and says, "your viral load is high," that's not good enough! If possible, check the results with a second test. The cash price is $125 to $200. In New York, Medicaid and ADAP pay for five tests the first year, and four every year after that.

Viral load tests are also used by doctors to decide when to suggest starting anti-HIV drug treatment in people without symptoms. Again, there's no general agreement on how to use viral load test results for this purpose. There's absolutely no hard information about when it's best to start anti-HIV drug treatment for someone without symptoms but with a detectable viral load.

There is definite evidence that people who are sick and have very low T-cell counts (below 50) can benefit greatly from anti-HIV drug treatment. But for people with higher T-cell counts, no symptoms and even with detectable viral load, all the reasons for and against starting treatment are theoretical.

Doctors who recommend starting treatment early do it because they believe it will stop or slow disease progression and prevent the ongoing destruction of the immune system.

But taking drugs for many years may be associated with toxicities that could offset any theoretical benefit. Also, there are only a limited number of drugs, and HIV can become resistant to all of them.

This may be more likely to happen if the drugs are taken irregularly, which could happen over many years of taking medication. So another possible danger from starting treatment early is that, because HIV has become resistant, the drugs will no longer work at later stages when they may be most needed.

The bottom line is that for people with high T-cells and no symptoms, no one knows when it's best to start treatment!

2. How Well Drugs are Working

Viral load tests are a great way to see if anti-HIV drugs are working. If your viral load goes down after starting anti-HIV drugs, then you know the drugs are hitting HIV. If your viral load goes up later, the drugs have stopped working as well. HIV has probably become resistant to at least one of the drugs in your combination. When this happens, you may have to change your drug combination.

Find out your viral load before starting an antiviral combination. Be sure you confirm the result with a second test before starting. Get another test one month after starting to be sure the drugs are working. For example, if your starting viral load is 100,000, your viral load one month later should be 1,000-a drop to 1/100th of what it was (also called a ten-fold drop). Get a test every three months to be sure the drugs are continuing to work.

The aim of treatment is to reduce the viral load. Some doctors want the viral load to be undetectable using the most sensitive tests (those that can detect more than 20 copies of HIV RNA). This is because theoretically there is less chance of HIV becoming resistant to the drugs when the viral load is low. But no one knows if this is the best approach.

It may be better in the long run to be content with keeping the viral load detectable but at a low number. If you change your combination every time your viral load increases above 20, or even above 400, there is a greater chance that you will run out of options more quickly.

Viral load tests are a new tool for understanding HIV infection. Most new drugs (protease inhibitors and drugs like Sustiva) were approved because they lower viral loads. It seems like a good idea to have less HIV in your blood. But as you can tell, there's a lot we don't know about how to use the viral load in deciding whether to start treatment, and when to change treatment.

We do not yet know the relationship between low viral load, good health, and length of survival. And one more important thing: Just because your viral load is undetectable, it doesn't mean you're not infectious.

So what's a good viral load?

Some people say undetectable, some say under 1,000 and some say under 40,000. Lots of theories, but no answers yet. Depending on what you believe, you might choose to take anti-HIV drugs in different ways. In order to figure out what's right for you, you're going to have to work closely with your doctor, and figure out what he or she thinks.

SO ASK 'EM: what do they think is a good viral load, what do they expect to happen, and by when? Remember, there are lots of possible ways to look at all this.

Here are three examples:

Super-duper model: Undetectable!

Taking anti-HIV drugs to keep viral load below "undetectable". This means:
  • taking 2-4 drugs, starting all of them at once or very close to each other.
  • checking your viral load a month later.
  • switching at least two drugs if your viral load starts to climb.


  • using up future drug options before necessary.
  • developing multi-drug-resistant HIV.
  • developing serious side effects.


  • radically lengthening the time you have without AIDS-related illnesses, and if you have AIDS, increased survival.


Middle-of-the-road model: Low and stable!

Taking anti-HIV drugs in combinations which keep viral load below 10,000. This means:

  • taking 2-3 drugs.
  • checking your viral load a month later.
  • switching at least two drugs if your viral load goes back up.


  • developing drug-resistant HIV quickly.
  • not hitting HIV hard enough to increase survival and time without illness.
  • using up options quickly if the treatment fails developing side effects.


  • using well-understood drug combinations with known side effects and interactions.
  • dropping viral load by ten-fold lessens progression by 30% the chance to benefit from future knowledge of which drugs really work well together.


What's the bottom line?

There are new theories about how HIV grows, and how to stop it from causing AIDS.

Theory: a set of ideas explaining why certain things happen. A theory is different from knowing for sure. It's messy. Theories might be right or wrong, and it takes time to find out.

Many people dismiss theories, but they could be right -- we just don't know. In time, we'll have a much better understanding of how best to treat HIV -- thanks to viral load tests, new drugs and the patience and intelligence of people living with HIV/AIDS.

Laid-back model: Wait and see!

Taking no anti-HIV drugs right now, since your viral load and immune system seem stable. This means:

  • checking your viral load at least every three months.
  • monitoring your health closely.


  • not preserving immune system strength, such as T-cells and thymus health.
  • allowing more HIV to grow in the lymph and central nervous system.
  • developing infections, which boost viral load.
  • coping with the fear of "doing nothing" in a culture that strongly believes in taking meds.


  • no side effects or long-term risk from drugs.
  • plenty of future options, including drugs not approved yet.
  • benefiting from future knowledge of how to best treat HIV
  • freedom from adhering to a complicated, demanding regimen.


Most people believe that a really high viral load, like 300,000 or a million, should be treated with a strong combination of drugs. The rest is a gamble. Most early theories about AIDS have been proven wrong over time. No one can really know for sure what the absolute best thing to do is. So ask as many questions as possible, learn about your health (T-cells, T-cell percents, etc.), believe in survival, and find as much love and support as you can.

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This article was provided by PWA Health Group.