What's happening?

You may feel ill for a while at this stage. This is often called 'seroconversion illness' because it coincides with the time that blood tests for antibodies to HIV become positive.

Once seroconversion has taken place, you may stay well for a number of years without treatment. But there will be some signs of damage being done to your immune system. And you are infectious during this period, even though you may not be aware you have HIV.

This damage can be detected by laboratory tests. Doctors will use two key tests at your regular clinic appointments:

CD4 cell count

This gives a rough indication of the strength of your immune system.

A normal CD4 cell count in an HIV-negative man is between 400 and 1600 per cubic millimetre of blood (but doctors normally just give a figure, e.g. 500). CD4 cell counts in HIV-negative women tend to be a little higher, between 500 and 1700.

Soon after infection with HIV, your CD4 cell count probably dropped sharply, before stabilising at around 500 to 600. Even while you are well and have no obvious symptoms of HIV, millions of CD4 cells are infected by HIV and lost every day, and millions more are produced to replace them. General illness can also impact upon your CD4 count, which may subsequently rise again. 

Without treatment, an HIV-positive person’s CD4 cell count will fall over time. 

Viral load test

This shows how active HIV is in your body.

The test for viral load measures how many particles of HIV are circulating in the blood. The results are given as the number of ‘copies’ of HIV per millilitre of blood; for example 200 copies/ml.

Your viral loads can fluctuate a lot if you’re not taking HIV treatment. Looking at the trend over a number of months may be more useful than comparing two test results.

A high viral load will usually – but not always – mean a low CD4 count. Knowing what is going on with your immune system can help you make decisions about lifestyle and treatment.