Prostate specific antigen

Prostate specific antigen (PSA) is currently used as a tumour marker for prostate adenocarcinoma.

PSA is a 33 kilodalton glycoprotein produced in prostate epithelial cells. Its normal physiologic role is as a liquefying agent for seminal fluid; only a tiny amount leaks into the blood, therefore its normal serum level is usually very low. Elevated serum levels of PSA have been associated with prostate carcinoma.

PSA can exist in the serum in two forms:

• bound/complexed (to serum protein): elevated levels are associated with prostate cancer
• free PSA (fPSA): elevated levels are associated with benign prostatic hyperplasia (BPH)

PSA levels

Although an increased PSA level is associated with prostate cancer, a low level cannot exclude prostate cancer. Although exact cut-off values are continually in flux, subject to the most recent data:

• 2-4 ng/mL: 15-25% change in a man >50 years old of having prostate cancer
• 4-10 ng/mL: imaging screening/biopsy indicated

The absolute level may also be misleading if there is a trend in the data upward (or downward) over time. Men with enlarged glands from BPH may also have elevated PSA levels. False-positive levels have been associated with

• benign prostatic hyperplasia
• prostate infection/prostatitis
• urinary tract infection
• manipulation (e.g. digital rectal exam or transrectal ultrasound)
• recent ejaculation

An upward trend in a patient's PSA value may also be concerning after a prostatectomy, raising suspicion for recurrent / metastatic/metastatic disease.

See also

• free/total PSA ratio
• PSA density