title: Stability and accuracy of total and free PSA values in samples stored at room temperature.
abstract: BACKGROUND
  In 2010, an estimated 476,076 total PSA tests were performed in Ireland, at a cost of €3.6 million with the majority ordered by general practitioners. We aimed to replicate storage conditions at room temperature and see if prolonged storage affected total and free PSA values.
  
  
  METHODS
  Blood samples were taken from 20 male patients in four VACUETTE®Serum Separator tubes (Greiner-Bio-One, Austria) and stored at room temperature (22 °C) for different time intervals (4, 8, 24, 48 h) before being centrifuged and analyzed. Total PSA (tPSA) and free PSA (fPSA) values were determined using the Tosoh AIA 1800 assay (Tokyo, Japan).
  
  
  RESULTS
  Mean tPSA values were measured at 4, 8, 24 and 48 h with values of 7.9, 8.1, 7.8 and 8.0 μg/L, respectively. Values ranged from -1.26 to +2.53 % compared to the initial 4 h interval reading, indicating tPSA remained consistent at room temperature. The tPSA showed no significance between groups (ANOVA, p = 0.283). Mean fPSA values at 4, 8, 24 and 48 h were 2.05, 2.04, 1.83, 1.82 μg/L, respectively. At 24 and 48 h there was 10.73 and 11.22 % reduction, respectively, in fPSA compared to the 4-h time interval, indicating prolonged storage resulted in reduced fPSA values. After 24 h, there was an 8.8 % reduction in the free/total PSA %. The fPSA showed significant differences between groups (ANOVA, p = 0.024).
  
  
  CONCLUSIONS
  Our recommendation is that samples that have been stored for prolonged amounts of time (greater than 24 h) should not be used for free PSA testing.
authors.affiliation: Department of Urology, St. James's Hospital, Dublin 8, Ireland. jamesforde@rcsi.ie.
authors.forename: J C
authors.initials: JC
authors.lastname: Forde
authors.affiliation: Department of Clinical Biochemistry, St. James's Hospital, Dublin 8, Ireland.
authors.forename: O
authors.initials: O
authors.lastname: Blake
authors.affiliation: Department of Clinical Biochemistry, St. James's Hospital, Dublin 8, Ireland.
authors.forename: V E
authors.initials: VE
authors.lastname: Crowley
authors.affiliation: Department of Urology, St. James's Hospital, Dublin 8, Ireland.
authors.forename: T H
authors.initials: TH
authors.lastname: Lynch
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D006801:Humans; D007494:Ireland; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood; D013048:Specimen Handling / Q000592:standards*; D013696:Temperature; D013997:Time Factors
chemical_list: D017430:Prostate-Specific Antigen
keywords: Free PSA; General practitioner; Prostate cancer; Storage; Total PSA