CD 4 test measures the CD 4 cells which are most affected by the HIV. As the HIV progresses, CD 4 count goes down. At a CD 4 count below 200 in diagnosed HIV patients, preventive treatment for AIDS should be started even if there are no symptoms of AIDS. Some doctors recommend start of preventive therapies at CD 4 count 350. So, a CD 4 count below 200 means AIDS in diagnosed HIV patient.
