Increase in percent free prostate-specific antigen in men with chronic kidney disease

Prostate-specific antigen (PSA) occurs in different molecular forms in serum: free PSA (fPSA) and complexed PSA (cPSA), the sum of which corresponds to total PSA (tPSA). In addition to tPSA, percent fPSA is widely used in the detection of prostate cancer. Free PSA, approximately 28 kDa, is eliminated by glomerular filtration. Previous data showed that men with end-stage renal dysfunction requiring chronic dialysis have increased percent fPSA. In this study, we evaluated whether moderate-to-severe chronic renal dysfunction, but with no need for dialysis, also importantly affects percent fPSA.

The study group consisted of 101 men (median age 57 years, interquartile range 46-68) with chronic kidney disease and no diagnosis of prostate cancer. Their median glomerular filtration rate (GFR) was 23 mL/min/1.73 m(2) (interquartile range 16-33; range 8-83), determined by iohexol clearance. Controls included 5264 men (median age 57 years, interquartile range 54-62) attending a prostate cancer screening program with no diagnosis of prostate cancer during 8 years of follow-up.

With adjustment for age, median fPSA levels and percent fPSA were significantly higher (P < 0.001) in patients with renal dysfunction, 0.45 microg/L and 47.2%, respectively, compared to controls, 0.29 microg/L and 29.9%, respectively. Regression analysis in the study group showed a significant association between GFR and percent fPSA (P = 0.036).

The percent fPSA is importantly influenced by moderately impaired renal function in men with chronic kidney disease. For such men, use of the current clinical decision limits for percent fPSA could cause some men with prostate cancer to be misdiagnosed as having benign disease, and therefore fPSA should not be used to diagnose prostate cancer in these patients.