title: Error calculation for the PSA quotient.
abstract: OBJECTIVE
  Prostate specific antigen (PSA) assays have significant measurement errors, but the error associated with the PSA quotient (free to total PSA) often remains unknown.
  
  
  METHODS
  We used both Gaussian error calculation and measurement of imprecision to investigate the level of error associated with the PSA quotient.
  
  
  RESULTS
  Surprisingly, we found that the error of the PSA quotient at low levels is markedly smaller than that of the total PSA value.
  
  
  CONCLUSIONS
  The PSA quotient should be calculated and considered as a clinically relevant value.
authors.affiliation: Institute of Clinical Chemistry and Laboratory Medicine, Johannes Gutenberg University, Mainz, Germany. arneth@zentrallabor.klinik.uni-mainz.de
authors.forename: Borros M
authors.initials: BM
authors.lastname: Arneth