The CD4/CD8 ratio is a reflection of immune system health. A normal ratio is between 1 and 4. People without HIV infection 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. People with autoimmune diseases tend to have an increased CD4/CD8 ratio, while those with viral infections have a decreased 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'. Long-term non-progressors and those 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.