A CD4 count is a lab test that measures the number of CD4 T lymphocytes (CD4 cells) in your blood. In people with HIV, it is the most important laboratory indicator of how well your immune system is working and the strongest predictor of HIV progression.
CD4 cells (often called T-cells or T-helper cells) are a type of white blood cells that play a major role in protecting your body from infection. They send signals to activate your body´s immune response when they detect intruders, like viruses or bacteria.
Your CD4 count is also used to help you and your HIV care provider decide when to start antiretroviral therapy (ART).
A CD4 count of fewer than 200 cells/mm3 is one of the qualifications for a diagnosis of stage 3 infection (AIDS)
500-1,200 cells/mm3 in healthy adults/adolescents
HIV viral load- provide valuable prognostic information of the patient on treatment. (link HIV viral load )
HIV Genotyping- provide information regarding the resistance developed in patient of HIV hence it help clinician to provide better Anti-retroviral treatment to patient. (link HIV Genotyping )