CD4 counts and viral load tests when on treatment
At least two weeks before every regular check-up you have at your HIV clinic, you will need to visit the clinic to give some blood. This blood is used to test for your CD4 count and your HIV viral load. The CD4 count gives you an indication of how your immune system is coping with HIV, and your HIV viral load tells you how active HIV is in your blood at the time of the test.

Don’t worry about minor fluctuations in the results from test to test as this is normal. It’s the long-term trends over time that will give you a picture of how active HIV is in your blood, and how your immune system is coping with HIV.

The way your HIV is monitored may differ if you agree to go onto a drug trial. We talk about drug trials in the section on HIV Treatment.

CD4 count
Your CD4 count tells you how many CD4 cells there are in a microlitre of your blood (a microlitre is equal to one millionth of a litre, or one cubic millimetre). This will give you an indication as to how strong your immune system is. Generally speaking, the more CD4 cells there are, the stronger your immune system is. Most men without HIV have CD4 counts anywhere between 500 and 1500. Generally, people with HIV are advised to start thinking about treatment if their CD4 count is on a downward trend and dropping to 350 or below.

The CD4 count is the main CD4 test result your doctor will give you. However, there are other ways to measure CD4 levels in your blood. You may come across one in particular called your CD4 cell percentage which some doctors regard as a more accurate way of measuring CD4 levels.

CD4 cell percentage
Your CD4 cell percentage tells you what proportion of all your white blood cells (known as lymphocytes) are CD4 cells. If your CD4 count drops, so will the CD4 cell percentage. Most people without HIV have a CD4 cell percentage of around 40%. Doctors would want you to think about starting HIV treatment before this percentage drops below 20%.

Viral load
Your viral load test will tell you how many copies of HIV are in a millilitre of your blood (a millilitre is equal to one thousandth of a litre, or one cubic centimetre). When your viral load is very high (anything above 100,000) it means that HIV is very active, and when this is the case it is more likely that your CD4 count will fall more rapidly than if your viral load was low. A viral load can range from less than 50 HIV copies per millilitre of blood (50 is the lowest number the current tests can detect) to numbers up into the millions.

A high viral load and a low CD4 count may indicate that you need to start thinking about treatment, but if the test results are your first since diagnosis it may instead indicate that you have been infected very recently. It is not uncommon to temporarily see a high viral load and low CD4 count in the initial stages of HIV infection.

We talk more about how HIV targets CD4 cells in the section on How HIV Works.

CD4 counts & viral load tests when on treatment
HIV treatment aims to slow or stop HIV from making more copies of itself, or replicating, in your blood. Your viral load would then start to fall allowing your body to replace lost CD4 cells at a quicker rate than HIV can destroy them. Your CD4 count would then start to rise again. CD4 counts and viral load tests continue to be used to monitor how effectively your HIV treatment is working and to see how well your immune system recovers.

If HIV treatment fails to suppress your viral load, this could indicate that the combination of anti-HIV drugs you are taking is not working as well as it should. You and your doctor would then probably start thinking about changing to a different and more effective combination of drugs.

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