Five PSA Methods Compared by Assaying Samples with Defined PSA Ratios,

Abstract
Prostate-specific antigen (PSA) has been established as a marker to aid in detection and monitoring of prostate cancer (1)(2). PSA in serum exists predominantly in three forms: free, uncomplexed PSA; PSA covalently complexed to α1-antichymotrypsin (PSA-ACT); and PSA covalently complexed to α2-macroglobulin (PSA-MG) (3). Immunoassays available today recognize free PSA and PSA-ACT but not PSA-MG, and their result for “total PSA” refers to the sum of the free and ACT-bound forms of PSA as measured by the immunoassay.