This laboratory test measures the total concentration of prostate-specific antigen (PSA) in blood serum. PSA is a glycoprotein produced primarily by the epithelial cells of the prostate gland. It exists in the blood in two forms: free (unbound) and bound to proteins. This test measures the total concentration of both forms. While PSA is elevated in cases of prostate cancer, it is also commonly elevated in benign conditions such as benign prostatic hyperplasia (BPH) and prostatitis.