The CD4/CD8 ratio is a reflection of immune system health.
CD4 cells (also known as CD4 lymphocytes or T-helper cells) help coordinate the immune response by stimulating other immune cells, such as macrophages, B lymphocytes (B cells), and CD8 cells to fight infection. Untreated HIV targets and destroys CD4 cells.
CD8 cells (also known as CD8 lymphocytes or T-suppressor cells) recognise and destroy cells infected with bacteria or viruses.
The CD4/CD8 ratio is calculated by dividing the CD4 cell count by the CD8 cell count. For example a ratio of 2 would indicate that there are 2 CD4 cells for every 1 CD8 cell. A normal ratio is between 1 and 3.
HIV-negative people generally have a greater number of CD4 cells than they have of CD8 cells. As people get older, the immune system's defence against pathogens is weaker and the CD4/CD8 ratio tends to decrease. Having a higher ratio is better than having a low ratio.
Within six months of seroconversion, the CD4 count generally decreases about 30% and the CD8 count may increase by about 40%, resulting in an inverted ratio that is generally less than 1. With antiretroviral treatment, the ratio may revert toward 'normal'. People who start antiretroviral treatment early on generally have a normal CD4/CD8 ratio.
Factors affecting CD4 count and subsequently the CD4/CD8 ratio are some viral infections, tuberculosis, corticosteroid use, seasonal/diurnal variations, and variations in CD4 analyses.
In usual clinical care of people living with HIV, the CD4 cell count is more important than the CD4/CD8 ratio. There's more information about CD4 cell counts on another page.