What are the normal PSA levels for a adult human?

PSA, or prostate-specific antigen, is a protein produced by the prostate gland. Normal PSA levels vary depending on age and other factors, but generally the reference range for PSA in adult males is considered to be between 0 and 4 nanograms per milliliter (ng/mL) of blood. However, it's important to note that PSA levels can fluctuate and may vary slightly between individuals, so a single elevated PSA level may not necessarily indicate a problem. If you have any concerns or are experiencing any symptoms, it's best to consult with a healthcare professional for personalized advice.