A CD4 count is a blood test to check how many CD4 cells are in your blood and how strong your immune system is. CD4 cell counts should be measured when you are diagnosed with HIV.
If you have HIV, a CD4 count is used to:
See how HIV is affecting your immune system. CD4 counts can help monitor your risk for developing Opportunistic Infections (OIs), such as TB or certain cancers.
Help check how well HIV treatment is working. A CD4 count is used with an HIV viral load test to see if HIV medicines are working. A viral load test measures how much HIV is in your blood.