Doctors use two key tests to assess the strength of your immune system – a CD4 cell count and a viral load test. HIV damages your immune system even though you may look and feel well. That’s why new guidelines recommend that everyone with HIV starts treatment whatever their CD4 count.
Viral load explained
The viral load test 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 load test results 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.
What’s happening inside you after infection?
When you first get HIV, your body starts to produce antibodies to fight it off.
You may feel ill for a while at this stage. This is often called ‘seroconversion illness’ because it coincides with the time that blood (‘sero’) tests for antibodies to HIV become (‘conversion’) 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.
As you can see on the graphic above, you will also be infectious during this period, even though you may not be aware you have HIV. That’s why it is so important to get diagnosed early, so you can start treatment as soon as possible – before too much damage has been done to your immune system.
The strength of your immune system can be detected by laboratory tests. Doctors will use two key tests at your regular clinic appointments – a CD4 cell count and a viral load test.
What is the CD4 cell count?
This test 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 have an impact on your CD4 count, which may subsequently rise again.
Without treatment, an HIV-positive person’s CD4 cell count will fall over time (see the graphic above).
Starting treatment – new guidelines
Recently the British HIV Association (BHIVA) treatment guidelines have been changed to say that anyone with HIV who is ready to commit to treatment should start regardless of their CD4 count. This reflects the findings of the START study.
START found that people who waited to start treatment until their CD4 count dropped to 350 (which is when people were previously advised to start) had a much higher chance of developing AIDS-related illnesses such as cancers.
Starting treatment also reduces the chances that you will pass on HIV.