CD4 cells (also known as CD4+ T cells) are white blood cells that fight infection. CD4 cell count is an indicator of immune function in patients living with HIV and one of the key determinants for the need of opportunistic infection (OI) prophylaxis. CD4 cell counts are obtained from bloodwork as part of laboratory monitoring for HIV infection.

CD4+ cell counts are usually measured when you are diagnosed with HIV (at baseline), every 3 to 6 months during first 2 years or until your CD4 count increases above 300 cells/mm³. Otherwise your CD4+ cell count may be measured every 12 months. Most people who are on HIV treatment can expect an average increase of about 50-100 cells/mm³ a year. Patients who initiate therapy with a low CD4 count or at an older age may not have the same increase in their CD4 count despite virologic suppression.

There are multiple factors that affect your CD4 count. Taking your medication is one way to keep your count high but medications or acute infections are among the things that could affect the CD4 count. If you are responding well to your medications, you may need less frequent testing going forward.