What is a CD4 count and what does it tell me?

What is a CD4 count and what does it tell me?

CD4 cells are the “bosses” of the immune system. They organize the battle against invading germs and viruses. Your CD4 count tells you how many CD4 cells you have: a “normal” CD4 count is anywhere from 600 to 1,200 cells/mm³. That’s how many CD4 cells are in a “cubic millimetre” of blood (about the size of a grain of rice).

If you have HIV, your CD4 count will probably be lower than normal. That may be OK—your immune system can still keep you healthy even with a CD4 count below normal. But a count of 200 or lower means a much greater danger of getting sick. Staying healthy means keeping your count well above 200.

CD4 counts are one of the biggest factors in deciding when to start treatment. When your CD4 count dips too low, your doctor will likely talk with you about your treatment options. You’ll also talk about treatment if you've already got serious HIV-related symptoms, no matter what your CD4 count is.

It’s a good idea to keep track of your CD4 counts on your own so you can see the patterns over time. You might want to ask your doctor for a copy of your blood test results.

Why would my CD4 count fall?

We mentioned that CD4 cells are the “bosses” of your immune system. The reason HIV is so serious is because it actually attacks the CD4 cells—the very thing your immune system depends on to stay strong and keep you healthy.

During infection, HIV enters your CD4 cells. HIV then turns these cells into little factories that make lots of new copies of the virus. The CD4 cells are killed in the process, and this happens over and over again. Over time, your body can’t produce enough CD4 cells to replace the ones killed, and so your CD4 count falls.