PSA Test (Prostate Specific Antigen)

  • Medical Author: Pamela I. Ellsworth, MD
  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Quick GuideScreening Tests Every Man Should Have

Screening Tests Every Man Should Have

What can lower the PSA test result?

Medications commonly taken to treat benign enlargement of the prostate (BPH) such as finasteride (Proscar), dutasteride (Avodart), and a combination of dutasteride and tamsulosin (Jalyn) can decrease the PSA by about 50% within six to 12 months of starting their use. Another medication used to treat fungal infections, ketoconazole, can also lower PSA levels. Lastly, herbal supplements such as saw palmetto and those containing phytoestrogens, which are plant-derived chemicals with estrogen-like effects, can also lower the PSA level. It is important to tell your health care provider all the medications, both prescription and nonprescription, as well as any herbal preparations or health supplements that you are taking.

What is the accuracy of the PSA test?

One of the limitations of the PSA test is that PSA is not specific to prostate cancer and that it can be affected by several common conditions such as benign enlargement of the prostate, inflammation, and infection of the prostate. Furthermore, there is some variability in PSA results when using different testing equipment. One study showed that 25% (one in four) men who had an initial PSA result between 4 ng/mL and 10 ng/mL had a normal test result when it was repeated.

Only about 25% of men who have an elevated PSA between 4 ng/mL and 10 ng/mL will have prostate cancer identified on prostate biopsy. If one uses a lower cutoff of 3.1 ng/mL, PSA had a sensitivity of 32% and specificity of 87% for identifying prostate cancer. Sensitivity refers to the likelihood of a positive test result if the individual has the disease, whereas specificity refers to the likelihood the test is negative if the individual does not have the disease.

Another concern in addition to the low specificity in detecting the presence of prostate cancer is the inability of the test to discriminate between a more aggressive prostate cancer from one that is less likely to cause harm. This is thought to lead to overtreatment in up to 50% of men with prostate cancer.

Medically Reviewed by a Doctor on 2/1/2017

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