[Analysis of biologic changes in PSA blood concentration and free PSA percentage in patients with normal rectal digital examination].
OBJECTIVE: To study intra-individual variations in serum PSA and percent free PSA in patients with normal digital rectal examination. MATERIAL AND METHODS: Analysis of changes in serum PSA levels and percent free PSA in two blood measurements conducted in 107 non-consecutive patients prior to prostate biopsy, over a period of time ranging from 23 to 60 days. Both total and free PSA were measured with two dual monoclonal antibody assays, Tandem-E and Tandem-R, Hybritech. Diagnosis was benign hyperplasia in 63 patients and cancer in 44. RESULTS: PSA variations ranged between -6.8 and +3.2 ng/ml in BPH patients, and between -2.8 and +9.0 when cancer was detected. The median coefficient of variation was 15.4 and 15.7, respectively. Variations in percent free PSA ranged between -30.7 and +40.9 in the BPH group and between -17.9 and +15.8 in the cancer group. The median coefficient of variation was 32.2 and 32.3%, respectively. Should prostate biopsy had been indicated when percent free PSA was equal to or lower than 25 in the 4 to 10 ng/ml PSA range, 15% patients would have exhibited discrepancies. Sensitivity would have ranged between 100 and 94.4%, with a reduction rate in negative biopsies between 16.6 and 19.4%. CONCLUSIONS: Intra-individual variations in serum PSA levels and percent free PSA may condition the decision of whether to perform a prostate biopsy.