title: Towards a consistent definition of a significant delta troponin with z-scores: a way out of chaos?
abstract: OBJECTIVE
  We assessed the diagnostic performance of z-scores to define a significant delta cardiac troponin (cTn) in a cohort of patients with well-defined clinical outcomes.
  
  
  METHODS
  We calculated z-scores, which are dependent on the analytical precision and biological variation, to report changes in cTn. We compared the diagnostic performances of a relative delta (%Δ), actual delta (Δ), and z-scores in 762 emergency department patients with symptoms of suspected acute coronary syndrome. cTn was measured with sensitive cTnI (Beckman Coulter), highly sensitive cTnI (Abbott), and highly sensitive cTnT (Roche) assays.
  
  
  RESULTS
  Receiver operating characteristic analysis showed no statistically significant differences in the areas under the curve (AUC) of z-scores and Δ with both superior compared to %Δ for all three assays (p<0.001). The AUCs of z-scores measured with the Abbott hs-cTnI (0.955) and Roche hs-cTnT (0.922) assays were comparable to Beckman Coulter cTnI (0.933) (p=0.272 and 0.640, respectively). The individualized Δ cut-off values that were required to emulate a z-score of 1.96 were: Beckman Coulter cTnI 30 ng/l, Abbott hs-cTnI 20 ng/l, and Roche hs-cTnT 7 ng/l.
  
  
  CONCLUSIONS
  z-scores allow the use of a single cut-off value at all cTn levels, for both cTnI and cTnT and for sensitive and highly sensitive assays, with comparable diagnostic performances. This strategy of reporting significant changes as z-scores may obviate the need for the empirical development of assay-specific cut-off rules to define significant troponin changes.
authors.affiliation: Pathology Queensland, Herston, Australia.
authors.forename: Carel J
authors.initials: CJ
authors.lastname: Pretorius
authors.forename: Louise
authors.initials: L
authors.lastname: Cullen
authors.forename: William A
authors.initials: WA
authors.lastname: Parsonage
authors.forename: Jaimi H
authors.initials: JH
authors.lastname: Greenslade
authors.forename: Jillian R
authors.initials: JR
authors.lastname: Tate
authors.forename: Urs
authors.initials: U
authors.lastname: Wilgen
authors.forename: Jacobus P J
authors.initials: JP
authors.lastname: Ungerer
mesh_terms: D054058:Acute Coronary Syndrome / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000175:diagnosis*; D012372:ROC Curve; D012015:Reference Standards; D014336:Troponin / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D014336:Troponin
keywords: Acute coronary syndrome; delta; diagnostic accuracy; myocardial infraction; troponin