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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 blood cells in a cubic millimetre 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 500 and 1500. But CD4 cell counts can vary a lot between people. Your own CD4 cell count can also vary and can go up and down in response to different factors. For example:

  • Women have higher CD4 cell counts than men (by about 100).
  • Women’s CD4 cell counts go up and down during the menstrual cycle.
  • Oral contraceptives can lower a woman’s CD4 cell count.
  • Smokers tend to have higher CD4 cell counts (by about 140).

None of these factors seem to make any difference to how well your immune system can fight infections.

Only a small proportion of your body’s CD4 cells are in the blood. The rest are in other organs, such as the spleen, and in lymph nodes. Variations in CD4 cell counts might be due to the movement of CD4 cells between blood and tissue.

So, rather than attach too much significance to an individual test result, it makes good sense to monitor any trends in changes to your CD4 cell count over time. It’s best to have your CD4 count measured at the same clinic and at roughly the same time of day wherever possible. If you have another infection, such as the flu or an outbreak of herpes, talk to your clinic about whether it is best to delay your CD4 count until you are feeling better. If you get a result that is very different to expected, your doctor may want to repeat the test to check whether the first result was a laboratory error.  

Soon after infection with HIV, your CD4 cell count probably dropped sharply, before stabilising. 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. Without treatment, an HIV-positive person’s CD4 count will fall over time.

A CD4 cell count between 200 and 500 indicates that some damage to your immune system has occurred.

It is particularly important to have your CD4 cell count carefully monitored as it gets closer to 350.

Having your CD4 cell count monitored

It’s recommended you have at least two CD4 cell counts done when you are first diagnosed with HIV. These results give you a ‘baseline’ level, so you and your doctor can assess changes in the future. These tests are likely to happen at your first HIV clinic visit and then at your first follow-up visit, between one and three months apart.

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 getting close to the level at which it’s recommended you start treatment (currently 350 for most people) or you are taking part in a clinical trial, your doctor may suggest that your CD4 count is monitored more often.

After you start HIV treatment for the first time, you will usually have a CD4 cell count about a month later, and then every three months. Once you have an undetectable viral load (see Viral load) and your CD4 cell count has started to increase, your doctor may suggest doing a CD4 cell count every six months. You can expect to have it checked more frequently if you have symptoms or become unwell.

Monitoring your CD4 cell count will help you and your doctor make important decisions about your HIV treatment and care.

CD4 cell count above 350 – monitor, and start treatment in some circumstances

If your CD4 cell count is above 350, generally you won’t need to be on HIV treatment. Your CD4 cell count will be monitored regularly, probably every four to six months. As your CD4 cell count starts to approach 350, your doctor may want to monitor you every three months.

In some situations, your doctor may recommend you start treatment when your CD4 cell count is still above 350. These include:

  • If you are also infected with the hepatitis B or C viruses, as liver disease becomes worse when the CD4 cell count is lower.
  • If you have heart problems or kidney disease.
  • If you are having treatment for cancer.
  • If you are older (for example, over 50).
  • If you want to start treatment because you are concerned about the risk of passing on HIV to someone else (treatment reduces the risk of HIV being passed on).
  • If you are ill because of HIV.
  • In some cases, if it is clear you have been very recently infected with HIV.

CD4 cell count of 350 – start HIV treatment

If your CD4 cell count falls to 350, it will usually be recommended that you start taking HIV treatment. Starting HIV treatment when your CD4 cell count is around 350 has been shown to have a number of advantages compared to waiting until your CD4 cell count is lower. The immune system is more likely to recover to levels normal for their age in people who start treatment when their CD4 cell count is around 350.

Starting treatment when your CD4 cell count is around 350 also means that you are very unlikely to become ill because of HIV. It has also been shown to reduce your risk of developing other serious illnesses as well, such as kidney and liver disease, as well as some cancers.

Your doctor will start talking to you about treatment when your CD4 cell count approaches 350. You may have more frequent CD4 cell counts during this time.

CD4 cell count of 200 or below – start HIV treatment and take other treatment to prevent infections

If your CD4 cell count is 200 or below, it is recommended you start treatment as soon as possible. A CD4 cell count of this level means that you are at risk of developing some serious illnesses.

You may also need to start taking other treatment to reduce the risk of these illnesses developing. This is called prophylaxis. The type of prophylaxis you’ll take will depend on your CD4 cell count. Your doctor will tell you when you can safely stop taking prophylaxis. This is generally once your CD4 cell count increases, usually to above 200, and stays above that for a period. For example, you might be given antibiotics (such as cotrimoxazole [Septrin] or dapsone) to prevent you developing PCP, a type of pneumonia.

You may have some additional tests if you have a lower CD4 cell count. This might include being tested for some infections and conditions, and can include screening for tuberculosis (TB). People from countries with a high incidence of TB will be screened for it whatever their CD4 cell count.

For more information on starting HIV treatment, see the NAM booklet Anti-HIV drugs.

Your CD4 cell count when you’re taking HIV treatment

Once you start taking HIV treatment, and your viral load starts to fall, your CD4 cell count is likely to increase gradually. The rate at which this happens can vary a lot between individuals. In some people, it can take months or even years for their CD4 cell count to climb towards normal levels for people of their age. If you started treatment with a low CD4 cell count, it’s more likely to take a long time for your CD4 cell count to go up. But it’s good to know that even quite small increases in your CD4 cell count can have big health benefits.

Your doctor will monitor your CD4 cell count, along with your viral load, every three months once you are on treatment. Once you have an undetectable viral load (see Viral load) and your CD4 cell count has started to go up, your doctor may suggest monitoring every six months.

CD4 percentage

In addition to using a test to count the number of CD4 cells, doctors sometimes measure the proportion of all white blood cells that are CD4 cells. This is called a CD4 cell percentage. Although it’s not recommended that CD4 percentages are used as a general indicator of the health of an adult’s immune system, there can be situations where it is a useful measurement. For example, if your CD4 percentage is very different to your CD4 cell count, it might be a sign of another health problem.

One circumstance when your doctor might measure your CD4 cell percentage could be if there is a big variation in your CD4 cell count between one test and the next.

CD4, viral load & other tests

Published July 2012

Last reviewed July 2012

Next review July 2015

Contact NAM to find out more about the scientific research and information used to produce this booklet.

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.