The PSA test is as invasive as a simple blood test, reports Mayo Clinic. Nurses or medical technicians must first draw blood with a needle before examining PSA levels in a laboratory. The most likely site of needle puncture is the arm.
PSA tests measure prostate-specific antigen, a type of protein produced in the prostate, according to Mayo Clinic. This protein also circulates in the blood in small amounts, and abnormally high levels may indicate prostate cancer. Conditions such as an inflamed prostate may also cause heightened PSA levels, so doctors may order a digital rectal exam for further diagnosis. Prostate biopsies can confirm prostate cancer. Once treatment begins for prostate cancer, PSA tests can provide feedback on effectiveness.