Can free and total prostate specific antigen and prostatic volume distinguish between men with negative and positive systematic ultrasound guided prostate biopsies?

Abstract

Purpose: We evaluated the role of free and total serum prostate specific antigen (PSA) and prostate volume in discriminating between men with negative and positive transrectal ultrasound guided biopsies.

Materials and methods: A total of 104 consecutive men with a positive biopsy and at least 3 mm. of prostate cancer was compared to 110 consecutive men with a negative biopsy. Prostate volume was determined by transrectal ultrasound. Total PSA was determined by the Tosoh AIA-600 PSA assay and free PSA was measured by the PSA II Dianon assay. We determined the free-to-total PSA ratio, free and total PSA densities, and the relationship of free PSA and free-to-total PSA ratio to prostate volume.

Results: Using a 23% cutoff value of free-to-total PSA, only 22.7% of biopsies were preventable in patients with a negative biopsy but 9.6% of the cancers were missed. At a total PSA of 4 to 10 ng./ml. 44.4% of the biopsy negative cases were correctly identified while missing 9.1% of the cancers if a 20% free PSA cutoff is used. For total PSA more than 10 ng./ml. an 18% free PSA cutoff properly identified 30.2% of the biopsy negative cases while missing 9.3% of the cancers. Percent free PSA is a better discriminant than prostate volume for total PSA more than 4 ng./ml. and the combination was not helpful. Free PSA density was identical in patients with negative and positive biopsies. There was no relationship between free PSA or free-to-total PSA ratio levels and prostate volume.

Conclusions: Use of a single discriminant criterion of free-to-total PSA ratio in the practical clinical setting of distinguishing negative and positive biopsies appears useful in patients with a total PSA of 4 to 10 ng./ml. Since free PSA is unrelated to prostate volume in biopsy negative and positive cases the physiological basis of free PSA is an enigma.