CD4 cell count
The CD4 cell count gives a rough indication of the strength of your immune system.
A normal CD4 cell count in an HIV-negative man is between 400 and 1600 per cubic millimetre of blood. CD4 cell counts in HIV-negative women tend to be a little higher, between 500 and 1700.
Soon after infection with HIV, your CD4 cell count probably dropped sharply. 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. General illness can also impact upon your CD4 count, which may subsequently rise again.
It is estimated, that without treatment, most HIV-positive people's CD4 cell count drops by about 45 cells every six months, with greater falls experienced by people with higher CD4 cell counts.