1. 7 CD4 count as a marker of your immune system
What is a CD4 count?
A CD4 count is the result of a blood test. It tells you how many CD4 cells are in a cubic millimetre of blood (mm3). Information about units of measure for blood tests.
The full medical name is a CD4+ T lymphocyte count. It is also called CD4+ T cell count or a T4 count.
Everyone should have a CD4 test when they are first diagnosed. The result can help estimate how long someone might have been HIV positive.
For many years, the CD4 count would be used to decide when to start HIV treatment (ART). For at least the last five years though, ART is recommended at any CD4 count, even if still very high.
- Most guidelines now say that all HIV positive people should use ART. This is both for individual health benefits and to reduce the risk of transmission.
- This is based on the START and TEMPRANO studies reported in 2015.
- A few countries still wait until the CD4 count drops below 500 cells/mm3. This is usually to save money.
Once on effective ART your CD4 count is now tested less often. So log as your are good at taking meds, this might only be once a year.
- Low CD4 counts might be tested more often.
- CD4 counts above 500 might only be tested every two years.
- This might vary in different countries.
What is a surrogate marker?
A surrogate marker is when one thing (that is easy to test) is used as a measure of something else (that is difficult to measure).
The CD4 count doesn’t directly measure HIV. But it is a good surrogate (or indirect) marker for how HIV has damaged your immune system. It can tell indicate the risk of infections.
The normal range for a CD4 count in an HIV negative person is between 400 and 1,600. This will cover 19 out of every 20 people (95%). But 1 in 20 HIV negative people (5%) have a normal CD4 count that is either less than 400 or higher than 1600.
HIV negative people outside this range are still very healthy. They do not have a stronger or weaker immune system. This is the range for a normal balance.
Pattern of CD4 count after HIV infection
- A few weeks after infection the CD4 count falls.
- Then the immune system begins to fight back. The CD4 count goes back up again, though not to as high as before HIV infection.
- The lowest level is usually 3 to 6 months after infection (if not on ART). This is called the CD4 set point. The lowest-ever CD4 count is also called the CD4 nadir.
- Without ART, the CD4 count will gradually drop. This usually takes several years. When not on ART, this is by roughly 50 cells/mm3 every year. In some people CD4 counts fall faster and in others much slower.
Most people can control HIV without treatment for many years.
However, without ART there is always a risk of serious infections. This is even with a high CD4 count. This is why guidelines recommend ART for everyone.
Last updated: 1 January 2021.