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Fact Sheet
Viral Load Tests

February 19, 2013

What Is Viral Load?

The viral load test measures the amount of HIV virus in your blood. There are different techniques for doing this:

Different test methods often give different results for the same sample. Because the tests are different, you should stick with the same kind of test to measure your viral load over time.

Viral loads are usually reported as copies of HIV in one milliliter of blood. The tests count up to about 1 million copies, and are always being improved to be more sensitive. The first bDNA test measured down to 10,000 copies. Current tests detect as few as 20 copies. Ultra sensitive tests for research can detect less than 5 copies.

The best viral load test result is "undetectable." This does not mean that there is no virus in your blood; it just means that there is not enough for the test to find and count. With the first viral load tests, "undetectable" meant up to 9,999 copies! "Undetectable" depends on the sensitivity of the test used on your blood sample.

The first viral load tests all used frozen blood samples. Good results have been obtained using dried samples. This will reduce costs for freezers and shipping.

How Is the Test Used?

The test is helpful in several areas:

How Are Changes in Viral Load Measured?


Repeat tests of the same blood sample can give results that vary by a factor of 3. This means that a meaningful change would be a drop to less than 1/3 or an increase to more than 3 times the previous test result. For example, a change from 200,000 to 600,000 is within the normal variability of the test. A drop from 50,000 to 10,000 would be significant. The most important change is to reach an undetectable viral load.

Viral load changes are often described as "log" changes. This refers to scientific notation, which uses powers of 10. For example, a 2-log drop is a drop of 102 or 100 times. A drop from 60,000 to 600 would be a 2-log drop.

Viral Load "Blips"

Recently, researchers have noticed that the viral load of many patients sometimes went from undetectable to a low level (usually less than 500) and then returned to undetectable. These "blips" do not indicate virologic failure or that the virus is developing resistance.

What Do the Numbers Mean?

There are no "magic" numbers for viral loads. We don't know how long you'll stay healthy with any particular viral load. All we know so far is that lower is better and seems to mean a longer, healthier life.

U.S. treatment guidelines (see Fact Sheet 404) suggest that all HIV-positive people be offered treatment. For patients with viral load over 100,000, there is urgency for treatment.

Some people may think that if their viral load is undetectable, they can't pass the HIV virus to another person. This is not true. There is no "safe" level of viral load. Although the risk is less, you can pass HIV to another person even if your viral load is undetectable.

Are There Problems With the Viral Load Test?

There are some concerns with the viral load test:

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