Effect of terminal renal failure on the ratio of free to total prostate-specific antigen

Objectives: To evaluate the effect of terminal renal failure on the ratio of free to total prostate-specific antigen (PSA). Methods: We measured free and total PSA in a group of 48 men on chronic hemodialysis. Samples were taken before dialysis and compared with a control group of 101 men without known prostatic or renal disease. Measurements of total and free PSA were made simultaneously with an ES-300 analyzer from Boehringer Mannheim according to the manufacturer's instructions. Results: Patients on hemodialysis have lower complexed PSA but higher free PSA than controls. Therefore, we observed a markedly higher calculated proportion of free PSA in the dialysis group (0.54 +/- 0.16 vs. 0.33 +/- 0.14, p < 0.00001). The calculated proportion of free PSA decreases progressively as the levels of total PSA increases from 0 to 4 mu g/l in both groups. By multivariate analysis, total PSA (p < 0.00001) and dialysis (p < 0.00001) were independent predictors of the fraction of free PSA. Age had no significant effect after correction for total PSA (p = 0.23). Conclusion: Patients on hemodialysis have normal total PSA but a significantly higher proportion of free PSA. Caution is therefore recommended for the interpretation of free PSA in that population since cutoff established in patients without renal disease may be inappropriate.