Free Prostate Specific Antigen

Prostatic secretory epithelium is the primary source of organ-specific PSA, which has long been recognised to be high in benign prostatic hyperplasia (BPH) and other non-malignant diseases. Several studies have reported a substantial difference in the percentage free PSA between individuals with prostate cancer and either benign disease or normal controls. Patients with tPSA readings in the "grey zone" of 4–10 ng/mL have shown improved sensitivity and specificity when using the ratio fPSA/tPSA.