Synonyms

   PSA Free/Total Ratio

   Prostate-Specific Antigen (PSA), Total and Free

Clinical Significance

   Assessing the risk of prostate cancer in patients with borderline or moderately increased total PSA (4.0-10.0 ng/mL)

   Determining which patients should have follow-up prostate biopsy

Specimen

   Serum

Stability

   Frozen (preferred) : 90 days

   Refrigerated : 72 days

Interpretation

   When total prostate-specific antigen (PSA) concentration is below 2.0 ng/mL, the probability of prostate cancer in asymptomatic men is low, further testing and free PSA may provide little additional information. When total PSA concentration is above 10.0 ng/mL, the probability of cancer is high and prostate biopsy is generally recommended.

   The total PSA range of 4.0 to 10.0 ng/mL has been described as a diagnostic "gray zone," in which the free PSA /Total PSA ratio helps to determine the relative risk of prostate cancer (see table). Therefore, some urologists recommend using the free PSA:total ratio to help select which men should undergo biopsy. However, even a negative result of prostate biopsy does not rule-out prostate cancer. Up to 20% of men with negative biopsy results have subsequently been found to have cancer.

   Based on free PSA:total PSA ratio: the percent probability of finding prostate cancer on a needle biopsy by age in years:

Limitation

   Normal results do not eliminate the possibility of prostate cancer. Tumor markers are not specific for malignancy. Test results cannot be interpreted as absolute evidence for the presence or absence of malignant disease.

   Specimens collected from patients undergoing prostate manipulation, especially needle biopsy and transurethral resection, may show erroneously high prostate-specific antigen (PSA) results. Care should be taken that specimens are obtained before these procedures are performed.