Question
What does my CD4 percentage mean?
7 January 2017. Related: All topics, CD4 and viral load.
Answer
Most information about how HIV affects your health comes from your CD4 count. This includes how HIV has damaged your immune system and how HIV treatment (ART) is making your immune system stronger.
The CD4 count is usually given as a number (usually between 1 to about 1600 cells/mm3).
This number is called the ‘absolute’ CD4 count.
However, many things affect this absolute number. These includes the time of the day, what you have eaten, if you have taken exercise, or if you have other infections. Each of these factors can affect your CD4 count but they are not related to immune system.
If your CD4 results are ever much higher or much lower than you expect, your doctor should look at your CD4 percentage (CD4%).
The CD4% can indicate whether this is a real change, or just a fluctuation. The CD4% is generally more stable.
The absolute CD4 count is still best at predicting risk of HIV progression.
The CD4% is the percentage of white blood cells that are CD4 cells. In an HIV negative adult the average CD4% is about 45%.(But this can range from 24% – 64%)
In adults, a CD4 percentage of 12-15% is considered similar to a CD4 count of 200 cells/mm3. A percentage of 15-20% is similar to an absolute count of 300 cells/mm3.
Babies and children with HIV are monitored using CD4%, because their absolute CD4 counts are much higher than adult counts, especially in the first few years.
CD4% may be an independent predictor of HIV disease progression, and a low CD4% should be considered as a factor in starting treatment, even when the absolute CD4 count is relatively ok.
This answer was updated in January 2017 from a question first posted on 8 October 2012.
Hi Sherif, it is great that you were able to start treatment so soon. How are you coping/feeling about being HIV positive?
This is a large variability in CD4 count. An absolute count can change during the day but CD4% remains more stable. Were you offered to do a third test? The most likely explanation is a lab error.
Within 2 years viral load can spike and then settle to a more stable number. E.g., spike to millions within the first few weeks and then the body has some immune response which causes the viral load to fall. There is no specific rate that CD4 count declines when HIV positive. Some people will lose their CD4 cells within the first few weeks, whereas others can go years without their CD4 count falling. How the body responds will be different to everyone.
The relationship between viral load and CD4 count is explained further here: https://i-base.info/ttfa/section-2/14-how-cd4-and-viral-load-are-related/