The Prostate-Specific Antigen (PSA), total (CPT 84153), is a fundamental laboratory assay used primarily in the context of urological health to measure the concentration of a specific glycoprotein in the blood. PSA, also known as gamma-seminoprotein or kallikrein-3, is produced by both normal and malignant cells of the prostate gland. In the healthy prostate, PSA is secreted into the seminal fluid to aid in the liquefaction of the semen coagulum, facilitating sperm motility. However, small amounts of PSA leak into the systemic circulation. When the architecture of the prostate gland is disrupted—due to conditions such as benign prostatic hyperplasia (BPH), prostatitis, or malignant neoplasms—the amount of PSA entering the bloodstream typically increases. The 84153 test measures the 'total' PSA, which encompasses both the free (unbound) form and the form complexed with protease inhibitors like alpha-1-antichymotrypsin (ACT). Clinically, this measurement is utilized in three primary capacities. First, it serves as a screening tool for prostate cancer, often in conjunction with a digital rectal examination (DRE), although its use for screening is subject to various professional guidelines (e.g., USPSTF, AUA) regarding age and frequency. Second, it is the cornerstone of monitoring patients with a confirmed diagnosis of prostate cancer. For those undergoing active surveillance, rising titers may trigger more invasive diagnostic procedures. For those who have undergone radical prostatectomy or radiation therapy, the PSA level is monitored to detect biochemical recurrence; following surgery, the level should ideally drop to undetectable levels. Third, it aids in the differential diagnosis of lower urinary tract symptoms (LUTS), helping clinicians distinguish between inflammatory, hyperplastic, or neoplastic causes of prostate enlargement. It is important to note that PSA is not cancer-specific but rather organ-specific. Various factors can transiently elevate PSA levels, including recent instrumentation of the urinary tract (e.g., cystoscopy), urinary tract infections, vigorous physical activity (like cycling), and recent ejaculation. Conversely, certain medications, specifically 5-alpha reductase inhibitors used for BPH (e.g., finasteride, dutasteride), can lower PSA levels by approximately 50 percent, necessitating a clinical correction factor when interpreting results.