title: Intraindividual variation of PSA, free PSA and complexed PSA in a cohort of patients with prostate cancer managed with watchful observation.
abstract: OBJECTIVE
  To determine the intraindividual variation of prostate-specific antigen (PSA) isoforms in prostate cancer patients managed conservatively with watchful observation.
  
  
  METHODS
  Patients with favorable clinical parameters (stage T1b-T2b N0 M0, Gleason score </= 7, and PSA </= 15) were recruited to participate in a watchful observation program. Specimens were drawn for measurement of total (tPSA), free (fPSA) and complexed (cPSA) prostate-specific antigen isoforms. Total biologic variation and between-day analytical variation were used to calculate intraindividual variation.
  
  
  RESULTS
  Total variation for each isoform and two ratios were not greatly affected by the time window for measurements in the interval 6 months to 2.7 yr. Analytical variation made only a small contribution to the total biologic variation. Intraindividual variation for a 1-yr time interval for tPSA, fPSA, cPSA and the ratios of fPSA and cPSA to tPSA was, respectively, 21.6, 19.3, 25.4, 20.0 and 13.1%. The amount of change required for a significant difference between two readings (with 95% confidence) was, respectively, 59.8, 53.4, 70.4, 55.3 and 36.2%.
  
  
  CONCLUSIONS
  There is a significantly higher intraindividual variation of cPSA (25.4%), and a significantly lower intraindividual variation of the ratio cPSA to tPSA (13.1%) compared to the other individual PSA isoforms and to the ratio of fPSA to tPSA. The amount of change required for a significant difference between two concentrations is large for all variables studied, but the lowest is the ratio of cPSA to tPSA (36.2%). These results have significance for diagnosis and monitoring of patients with prostate cancer.
authors.affiliation: Department of Clinical Pathology, Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario, Canada. psbunting@ottawahospital.on.ca
authors.forename: Peter S
authors.initials: PS
authors.lastname: Bunting
authors.forename: Gerrit
authors.initials: G
authors.lastname: DeBoer
authors.forename: Richard
authors.initials: R
authors.lastname: Choo
authors.forename: Cyril
authors.initials: C
authors.lastname: Danjoux
authors.forename: Laurence
authors.initials: L
authors.lastname: Klotz
authors.forename: Neil
authors.initials: N
authors.lastname: Fleshner
mesh_terms: D015331:Cohort Studies; D018450:Disease Progression; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D017430:Prostate-Specific Antigen / Q000032:analysis* / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000145:classification / Q000378:metabolism* / Q000473:pathology; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D017430:Prostate-Specific Antigen