CD4 cell counts

What CD4 cells do

CD4 cells, sometimes also called T-cells, or T-helper cells, are white blood cells which organise the immune system’s response to bacterial, fungal and viral infections.

CD4 cell counts in people without HIV

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 1500.

Even if you don’t have HIV, many factors can affect your CD4 cell count. For example, it’s known that:

  • 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).
  • CD4 cell counts fall after rest – by as much as 40%.
  • A good night’s sleep can mean that you have a lower CD4 cell count the following morning, but a higher CD4 cell count the next afternoon.
  • Physical activity can affect CD4 cell counts.

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 the lymph nodes and tissue. Variations in CD4 cell counts might be due to the movement of CD4 cells between blood and tissue.

CD4 cell counts in people with HIV

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 your CD4 cells are becoming infected by HIV and millions more are produced to replace them.

However, without treatment, most people will not be able to make enough new CD4 cells to replace those lost because of HIV. It’s estimated that without treatment, an HIV-positive person’s CD4 cell count drops by about 45 every six months, with greater falls experienced by people with higher CD4 cell counts at the time they became HIV positive.

A CD4 cell count between 200 and 500 indicates that some damage to your immune system has occurred – more than the normal ups and downs of CD4 cell counts. Steeper falls in CD4 cell counts are experienced the longer you have had HIV, and more significant damage is done to your immune system. This means you are at greater risk of becoming ill because of HIV.

A CD4 cell count of below 200 indicates that you are at real risk of becoming ill with an HIV-related illness. This is why you are recommended to have your CD4 cell count carefully monitored if it goes below 350.

It seems that people who experience a larger drop in CD4 cell count at the start of their HIV infection, and whose CD4 cell count stabilises at a lower level, may be at risk of faster disease progression.

Looking at your CD4 cell count can provide a guide for decisions about your need to start taking HIV treatment, as well as other medicines to prevent some HIV-related illnesses.

Your CD4 cell count can naturally fluctuate, and factors such as having a viral infection can affect it. Don’t put too much emphasis on a single test result. Rather, look at the trend in a number of recent CD4 cell counts.

If your CD4 cell count is high, and you have no symptoms and are not on HIV treatment, then it probably only needs monitoring every four to six months.

However, if it’s falling rapidly, you are unwell, or you are taking part in a clinical trial, it’s likely to be monitored more often.

CD4 cell percentages

Sometimes, as well as measuring the number of CD4 cells, doctors will also assess what percentage of all your white blood cells are CD4 cells. This is called the CD4 cell percentage. A normal result in a person with an intact immune system is about 40%, and a CD4 cell percentage below 20% indicates the same risk of becoming ill with an HIV-related illness as a CD4 cell count of about 200.

CD4 cell counts and HIV treatment

Your CD4 cell count can be used to help decide when you need to start HIV treatment, and as an indication of how successful these treatments are.

Treatment guidelines produced by the British HIV Association (BHIVA, the UK’s advisory body on HIV medical care) recommend that people with a CD4 cell count of 350 or below start HIV treatment as soon as they are ready.

In some situations, you may be advised to start treatment whatever your CD4 count is; for example:

  • If you have had an AIDS-defining diagnosis, such as certain cancers.
  • If you have heart problems, HIV-related kidney disease or HIV-related neurocognitive (brain) illnesses.
  • If you are having treatment for cancer that suppresses your immune system, such as chemotherapy.
  • In some cases, if you have hepatitis B and need treatment for that condition.

If you are also infected with the hepatitis B or hepatitis C virus, it is recommended that you start treatment when your CD4 cell count is around 500, as liver disease becomes worse when the CD4 cell count is lower.

If your CD4 cell count is below 200, your doctor will recommend starting HIV treatment very soon, ideally within two weeks. A CD4 cell count of below 200 indicates that you are at real risk of becoming ill with an HIV-related illness.

If you start treatment when your CD4 cell count is around 350, you are likely to respond well to HIV treatment. What’s more, starting treatment at 350 reduces the long-term risk of some serious, non-HIV-related illnesses like heart, liver and kidney disease.

Once you start HIV treatment, your CD4 cell count should start to increase slowly. If you experience a fall in your CD4 cell count over a number of tests, this should alert your doctor that there may be a problem with your HIV treatment.

You can find out more about starting HIV treatment in the section HIV treatment.

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.