[Analysis of biologic changes in PSA blood concentration and free PSA percentage in patients with normal rectal digital examination]. 
To study intra-individual variations in serum PSA and percent free PSA in patients with normal digital rectal examination.  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.  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%.  Intra-individual variations in serum PSA levels and percent free PSA may condition the decision of whether to perform a prostate biopsy.