Clinical Importance

Getting Tested
-Considerations
-Who should be tested
-How often
-Viral Load Results
-References

Slide Rule

Viral load is usually reported as copies per millilitre of blood plasma (copies/mL). Viral load levels can range from less than 50 copies/mL to 20 million copies/mL and higher.

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Changes in viral load are often reported as logarithmic or ‘log changes'. This is a mathematical term that refers to a change in the value of what is being measured by a factor of ten.

For example, if the initial viral load was 20,000 copies/mL, then a one log increase equals a ten fold (ten times) increase or 200,000 copies/mL. (The effect is the same as adding one zero to the original value). An increase of two logs equals a 100 fold (100 times) increase or 2,000,000 copies /mL. (The effect of adding two zeros to the original value).

In the same way, a one log decrease from the starting point of 20,000 copies/mL means that the viral load has dropped to 2,000 copies/mL. (The effect is the same as subtracting one zero from the original value). A two log decrease would indicate that viral load is now 200 copies/mL (subtract two zeros from the original value).

For help in calculating log values from RNA copies / mL please click here

Understanding the Results

Viral load measurements can assist doctors and people with HIV in deciding when to start anti-HIV treatment and help them assess whether treatment is working or not. This can be vital in managing HIV therapy options.

However, results of viral load tests can be interpreted differently by different doctors and HIV positive individuals. To help them decide what course of action to take, the National Institute of Health (NIH) in the US has developed some guidelines on when to initiate or alter antiviral therapy.

The main principals in the NIH document for interpreting viral load tests are:

• ‘Undetectable' viral load does not mean the virus has been eliminated, but that the level of virus in the blood is below the sensitivity of the viral test being used. The virus may be present in parts of the body that are harder to access, such as the lymph tissue and the brain.

• A result below 10,000 to 20,000 copies/mL is generally considered low, while 50,000 copies/mL and above is considered high.

• A change in viral load less than three fold is not considered to be significant. This means if viral load goes up from 5,000 to 15,000 individuals should not worry.

• If viral load is more than 20,000 the doctor should start a treatment programme.