CD4 cell counts

CD4 cells (sometimes called T-cells, or helper cells) are white blood cells that organise your immune system’s response to infections.

Your CD4 cell count is the measurement of the number of CD4 cells in a cubic millilitre of blood (a very small blood sample), not your whole body. Your doctor will probably just talk about your CD4 cell count as a number.

The CD4 cell count of a person not infected with HIV can be between 450 and 1600. But CD4 cell counts can vary a lot between people. For example, women tend to have higher CD4 cell counts than men.

Your own CD4 cell count can also vary and can go up and down in response to stress, smoking, the menstrual cycle, the contraceptive pill, recent physical activity, or even the time of day. It will also go down if you have an infection or illness.

So rather than attach too much significance to an individual test result, it makes good sense to monitor the trend in your CD4 cell count over time. It’s also best to have your CD4 count measured at the same clinic and at roughly the same time of day wherever possible. If you have an infection, such as the flu or an outbreak of herpes, it is best to delay your CD4 count until you are feeling better.

If you have a relatively high CD4 count, no symptoms and you are not taking anti-HIV drugs, your CD4 count will only be measured once every three or four months (or every six months if it is very high).

However, if your count has been falling rapidly, or you are taking part in a clinical trial, your doctor may suggest that your count is monitored more often.

The frequency with which your CD4 count is monitored after you start HIV treatment will depend on your clinic and how high your CD4 cell count is. As a general rule, you can expect to have it checked every three to six months and more frequently if you have symptoms or become unwell.