Repeat ultrasound guided prostate needle biopsy: use of free-to-total prostate specific antigen ratio in predicting prostatic carcinoma

Despite being the most useful tumor marker for the diagnosis of patients with prostate cancer, serum prostate specific antigen (PSA) is still hampered by lack of specificity. A negative prostate biopsy is associated with a 20 to 40% incidence of positive repeat biopsy in men with persistently elevated serum PSA levels. We determine whether the free-to-total PSA ratio could be predictive of prostate cancer in men undergoing repeat biopsy.

Archival sera, drawn before the first biopsy, were gathered from 51 men with a total serum PSA of 2 to 15 ng./ml. who underwent repeat prostate needle biopsy for various indications. The percent free PSA was calculated using the Hybritech Tandem-Rt free and total PSA as well as Dianon Systems freet and Hybritech total PSA assays. The free-to-total PSA ratio results between the cancer and noncancer groups were compared using Student's t test.

The median Hybritech free-to-total PSA ratio was significantly lower in patients with positive repeat prostate needle biopsy compared to those with negative biopsy (14.9 versus 19.4%, p=0.05). Total PSA as well as the percent Dianon free-to-Hybritech total PSA ratio were not significantly different between the 2 groups of men.

For total PSA in the range of 2 to 15 ng./ml. Hybritech free-to-total PSA ratio appeared to aid in the prediction of cancer on repeat biopsy.