Factors affecting CD4 counts
| Transient reductions | Diurnal variation in normal donors, reciprocating serum cortisol26 |
| Physiological stress (for example, post operative, immediately after exercise,27 or during bereavement)28 | |
| Exogenous steroids | |
| Cytotoxic drugs | |
| Intercurrent infections (for example, urinary tract infection and influenza) | |
| Transient increases | Women in follicular phase of the menstrual cycle29 |
| Long term reductions | Systemic lupus erythematosus (possibly because of apoptosis30) |
| Sarcoidosis (margination into tissues31) | |
| Primary immunodeficiencies | |
| Long term increases | Smoking29 |