title: Prostate specific antigen variation in patients without clinically evident prostate cancer.
abstract: OBJECTIVE
  We address long-term within individual variation of serum prostate specific antigen (PSA) in men without clinical or biopsy evidence of prostate cancer.
  
  
  METHODS
  We studied 943 men from a prostate cancer screening program with 2 PSA (PSA1 and PSA2) measurements available. A third PSA (PSA3) was obtained from 571 men. Only participants with no clinical evidence of cancer were included in the study. Within individual PSA variability was calculated based on indexes of percent coefficient of variation, ratio difference and PSA velocity. The relationship among these indexes, interval between measurements and number of PSA samples was assessed.
  
  
  RESULTS
  Mean interval was 670.4 days between PSA1 and PSA2, and 801.8 days between PSA2 and PSA3 (p<0.001). Mean coefficient of variation was 18% after 2 and 15.7% after 3 PSA measurements. Mean ratio differences were -0.047 ng./ml. for 2 and 0.033 ng./ml. for 3 samples. Mean PSA velocity was -0.128 ng./ml. per year for 2 and -0.055 ng./ml. per year for 3 samples, with 95% confidence intervals of 0.634 and 0.315, respectively. Variability was higher if only 2 PSA measurements were done (p<0.001). No clear relationship was found between individual variability and interval between measurements.
  
  
  CONCLUSIONS
  PSA velocity is within normal limits in almost all men (more than 95%) without clinically relevant prostate cancer. PSA individual variability is not fully dependent on the time between measurements when intervals are long, and can be substantially decreased with a third PSA sample.
authors.affiliation: Department of Urology, Hospital Universitario de Getafe, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Lujan
authors.forename: A
authors.initials: A
authors.lastname: Paez
authors.forename: E
authors.initials: E
authors.lastname: Sanchez
authors.forename: A
authors.initials: A
authors.lastname: Herrero
authors.forename: E
authors.initials: E
authors.lastname: Martin
authors.forename: A
authors.initials: A
authors.lastname: Berenguer
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000175:diagnosis; D013997:Time Factors
chemical_list: D017430:Prostate-Specific Antigen