title: Biological variation of total, free and percent free serum prostate specific antigen levels in screening volunteers.
abstract: OBJECTIVE
  We determined the biological variation of the total, free and percent free serum prostate specific antigen (PSA) in men 50 years old or older.
  
  
  METHODS
  Between July 1995 and February 1996 we studied 84 healthy men from our PSA screening study to determine biological variation by calculating the coefficients of variation of 3 PSA measurements on blood samples drawn from each subject 2 weeks apart.
  
  
  RESULTS
  The mean coefficients of variation for total, free and percent free serum PSA were 15, 17 and 14%, respectively. Age, total PSA and ejaculation were not confounding factors in this analysis (that is multivariate R2 less than 5% for all indexes).
  
  
  CONCLUSIONS
  There is a mean variation of approximately 15% in measurements of total, free and percent free PSA that does not appear to be significantly affected by age and total PSA level.
authors.affiliation: Division of Urologic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Ornstein
authors.forename: D S
authors.initials: DS
authors.lastname: Smith
authors.forename: G S
authors.initials: GS
authors.lastname: Rao
authors.forename: J W
authors.initials: JW
authors.lastname: Basler
authors.forename: T L
authors.initials: TL
authors.lastname: Ratliff
authors.forename: W J
authors.initials: WJ
authors.lastname: Catalona
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008403:Mass Screening; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood / Q000517:prevention & control; D012016:Reference Values
chemical_list: D017430:Prostate-Specific Antigen