PSA is a glycoprotein enzyme belonging to the kallikrein-related peptidase family, specifically kallikrein-3 (KLK3). It is secreted by the epithelial cells of the prostate and is primarily responsible for liquefying semen, aiding sperm motility. In the bloodstream, PSA exists in two main forms: free PSA (not bound to proteins) and complexed PSA (bound to proteins). The ratio of these forms can provide valuable diagnostic information. Smaller amounts of PSA also enter the bloodstream. Normal levels of PSA in the blood are usually very low. It has a molecular weight of approximately 34 kDa. Generally, PSA levels below 4 ng/mL are considered normal. However, normal ranges can vary based on age, race, and other factors. Elevated levels of PSA can indicate various pathological processes in the prostate. Screening guidelines for PSA differ among organizations. Some recommend screening for men over 50 years old, while others suggest considering screening for men over 45 years old with additional risk factors, or even 40 years old for high-risk groups. Measuring PSA levels helps assess the risk of prostate cancer, but elevated levels alone are not sufficient for diagnosis. Free PSA (fPSA) (not bound to other proteins) can help differentiate between benign and malignant prostate conditions. Low levels of free PSA can be a sign of cancer. PSA density is calculated as the ratio of PSA level in the blood to the prostate size measured by ultrasound. High density can indicate cancer. After surgical or radiation treatment for prostate cancer, PSA is monitored to track the success of the treatment. It is normal for PSA to drop to very low levels after successful treatment. An increase in PSA levels after they have been low can indicate a recurrence of the disease. Elevated PSA levels can be caused by benign conditions such as benign prostatic hyperplasia (BPH) or prostatitis. PSA levels naturally increase with age. Additionally, some medications and medical procedures can affect PSA levels. Prostate-specific antigen (PSA) is a crucial tool in diagnosing and monitoring prostate cancer, but its use requires careful consideration. Integrating PSA testing with other diagnostic methods and a personalized approach for each patient can help optimize treatment and improve patient quality of life.