PSA free
Prostate specific antigen (PSA) is a single-chain glycoprotein. Pathologically increased production of PSA is typical marker of malignant prostatic tissues and of bone metastases of prostatic origin. Increased levels of PSA are found also in patients with prostate benign hyperplasia. PSA occurs in three main forms in serum - free (fPSA), PSA bound on a2-macroglobulin and PSA bound on a1-antichymotripsin. The complex of PSA and a2-macroglobulin is immunologically inactive, and thus non-detectable by immunoassays, while two other forms are immunogically detected. The determination of free PSA can be be used, in combination with total PSA, for differential diagnosis between prostate cancer and benign prostate hyperplasia.