Interpreting viral load results

Understanding logs

A viral load result is usually described in terms of the number of HIV RNA copies per millilitre of blood (copies/ml). These numbers are often written in a form known as the logarithmic scale, such as 105. This means that the actual number is 10 x 10 x 10 x 10 x 10. Another way of thinking of 105 is as 1 with the decimal point moved five places to the right, the same as 1 plus 5 zeros – 100,000. Viral load variations can also be described using log changes. For example:

  • A decrease in viral load from 40,000 to 4000 copies could be described as a one-log decrease, a tenfold decrease, or a decrease of 90%.
  • A decrease in viral load from 40,000 to 400 copies could be described as a two-log drop (102), equivalent to a hundredfold fall.
  • A decrease in viral load from 40,000 to 40 copies would be a three-log drop (103), equivalent to a thousandfold fall.

Fractions of logs are hard to remember because they do not correspond to round number percentages. For example, a 0.5 log fall in viral load is a 66.6% decrease or a two-thirds fall in viral load. A 1.5 log fall is approximately a 96% reduction.

Scientific notation is a useful way for researchers to present data that include a wide range of values.

Community Consensus Statement on Access to HIV Treatment and its Use for Prevention

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.