1. 7 CD4 count as a surrogate marker
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 count soon after they are diagnosed with HIV. The result can help estimate how long someone might have been HIV positive.
The CD4 count used to be used for deciding when to start HIV treatment (called ART). In 2020 though, ART is recommended at any CD4 count, even if still very high.
- Most guidelines now say that treatment can be started at any CD4 count, including when over 500. This is based on reducing HIV transmission as well as health benefits to the person taking treatment.
- This change to earlier treatment came after the results of the START and TEMPRANO studies in July 2015.
- A few guidelines only recommend treatment when the CD4 count drops below 500 cells/mm3. This is usually for financial reasons.
How often your CD4 count is tested depends on:
- Current CD4 count. Lower CD4 counts are likely to need more frequent testing.
- Whether or not you re on ART. Once on ART, viral load tests are more important than the CD4 count, especailly if your CD4 count is above 350.
- Guidelines in your region or country.
What is a surrogate marker?
A surrogate marker is when one thing (usually that is easy to measure) is used as a measure of something else (that is difficult to measure directly).
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 range covers 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.
For HIV negative people, having a higher or lower CD4 does not mean 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 with HIV 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 infections (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 – usually over several years. When not on ART, the CD4 count drops by an average 50 cells/mm3 every year. In some people CD4 counts will fall much faster and in some people much slower.
In most people, the immune system can control HIV without treatment for many years.
However, untreated HIV increasse the risk of serious infections even with a high CD4 count. This is why in 2015 most guidelines changed to recommend ART for all HIV positive people.
Last updated: 1 January 2016.