1. 9 Interpreting CD4 results: CD4 count and CD4 percentage
A CD4 count is the number of CD4 cells in a cubic millimetre (cells/mm3).
This is sometimes written as cells in a microlitre (cells/µL) of blood or as cells x 106/L. Information about units of measure for blood tests.
A CD4 count is sometimes called an absolute CD4 count, because it counts the actual number of cells in a blood sample.
A single CD4 count doesn’t tell you very much. You really need to get several results over time to see the trend.
CD4 counts fluctuate. They go up and down during the day. For example, CD4 counts are lower when you first wake up and higher later in the day.  They are higher immediately after exercise – even running up and down stairs. They can also be affect by diet, whether you have other infections or even if there were just more or fewer cells in that sample of blood. None of these variations mean that your immune system is stronger or weaker.
This is why the trend of CD4 results is more important than any single count. The trend looks at the average of several results.
When you have several results you can see whether the trend is going up or down and how quickly it is changing – or whether it is generally stable.
CD4 count trend if not on ART
For someone who is not on ART, the CD4 count will generally be going down over time. This will be happening in people who are not yet diagnosed.
Each point on the dotted line shows an individual (absolute) CD4 count.
The solid line shows the average of these results. This example shows that the trend is for the CD4 count to fall over time. Even though the absolute number will be sometimes be higher than the previous result, the trend is more important.
In someone on effective ART, the trend will usually be going up. Individual CD4 counts can sometimes be lower than the previous result, but so long as viral load is still undetectable, the difference in not important.
If your CD4 count is above 500 on ART, many hospitals stop testing CD4 and only monitor using the viral load test.
CD4 percentage (CD4%)
The CD4 percentage (CD4%) is the percentage of white blood cells (lymphocytes) that are CD4 cells.
The immune system contains lots of different cells. The two main types of lymphocytes are T cells and B cells. CD4 cells are a type of T cell. So the CD4% looks at the CD4 count in relation to other immune cells.
CD4% is sometimes a more stable indication of whether there has been a change in the immune system. An unexpected drop in CD4 count when the percentage hasn’t changed indicates this drop is not clinically significant.
- A CD4% of 12-15% is about the same as a count of under 200 cells/mm3.
- A CD4% of 29% is about the same as a count of over 500 cells/mm3, but there is a wider range for higher values.
- The average normal CD4 percentage for someone who is HIV negative is about 40%. The normal range is anywhere from about 25% to 65%.
The CD4% count is used to monitor children under 12 years old. This is because you are born with very high CD4 levels. A baby can have a CD4 count that is 3000 cells/mm3.
- Carmichael KF et al. Analysis of diurnal variation of lymphocyte subsets in healthy subjects in the Caribbean, and its implication in HIV monitoring and treatment. Afr J Med Med Sci. 2006 Mar;35(1):53-7.
Last updated: 1 January 2016.