The PSA test is a blood test that measures the level of prostate-specific antigen (PSA), a protein made by the prostate, in a sample of your blood. A small amount of PSA normally circulates in the blood.
It is used to screen for prostate cancer and to help evaluate the cause of prostate conditions that are not cancer. A provider may also order it if the prostate feels abnormal on exam, and to monitor people during or after prostate cancer treatment; a screening test cannot by itself diagnose cancer, so further tests are needed if it finds a possible sign.
There is no single universally "normal" or "abnormal" PSA level. MedlinePlus notes that a level up to about 4.0 ng/mL has traditionally been considered normal, but this varies by age (PSA is often lower in men in their 50s and younger and tends to be slightly higher in older men). These figures are general reference points only and can differ by laboratory, age, sex, and testing method — your own lab report and its stated reference range are what apply to you. A number on its own is not a diagnosis.
A higher-than-expected PSA is not proof of cancer; the test cannot tell the difference between cancer and noncancerous causes. In general, the higher the level, the greater the chance that cancer is present, but higher PSA may also be seen with an enlarged prostate (benign prostatic hyperplasia, or BPH); prostatitis (inflammation of the prostate); a urinary tract infection; certain medicines; and temporary causes such as recent ejaculation or intercourse, a recently placed catheter, or recent procedures involving the bladder or prostate (for example cystoscopy or biopsy). This is a general, not complete, list of possible associations, and it is possible to have a high PSA without prostate cancer.
A low PSA is generally considered reassuring, and MedlinePlus does not describe low PSA as a distinct concern or typically report it as an abnormal "low" result. However, MedlinePlus notes it is possible (uncommonly) to have a low PSA and still have prostate cancer, which is one reason results are always interpreted in context rather than by the number alone.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.