Prostate-specific antigen, or PSA, is a protein produced by normal, as well as malignant, cells of the prostate gland. The PSA test measures the level of PSA in a man's blood. For this test, a blood sample is sent to a laboratory for analysis. Alpha 1-antichymotrypsin (symbol α1AC, A1AC, or a1ACT) is an alpha globulin glycoprotein that is a member of the serpin superfamily. In humans, it is encoded by the SERPINA3 gene.