title: Use of observed within-person variation of cardiac troponin in emergency department patients for determination of biological variation and percentage and absolute reference change values.
abstract: BACKGROUND
  Many patients presenting to the emergency department (ED) for assessment of possible acute coronary syndrome (ACS) have low cardiac troponin concentrations that change very little on repeat blood draw. It is unclear if a lack of change in cardiac troponin concentration can be used to identify acutely presenting patients at low risk of ACS.
  
  
  METHODS
  We used the hs-cTnI assay from Abbott Diagnostics, which can detect cTnI in the blood of nearly all people. We identified a population of ED patients being assessed for ACS with repeat cTnI measurement who ultimately were proven to have no acute cardiac disease at the time of presentation. We used data from the repeat sampling to calculate total within-person CV (CV(T)) and, knowing the assay analytical CV (CV(A)), we could calculate within-person biological variation (CV(i)), reference change values (RCVs), and absolute RCV delta cTnI concentrations.
  
  
  RESULTS
  We had data sets on 283 patients. Men and women had similar CV(i) values of approximately 14%, which was similar at all concentrations <40 ng/L. The biological variation was not dependent on the time interval between sample collections (t = 1.5-17 h). The absolute delta critical reference change value was similar no matter what the initial cTnI concentration was. More than 90% of subjects had a critical reference change value <5 ng/L, and 97% had values of <10 ng/L.
  
  
  CONCLUSIONS
  With this hs-cTnI assay, delta cTnI seems to be a useful tool for rapidly identifying ED patients at low risk for possible ACS.
authors.affiliation: ACT Pathology, Garran, ACT, Australia;
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Simpson
authors.affiliation: ACT Pathology, Garran, ACT, Australia; Australian National University Medical School, Canberra, ACT, Australia;
authors.forename: Julia M
authors.initials: JM
authors.lastname: Potter
authors.affiliation: ACT Pathology, Garran, ACT, Australia; University of Canberra, Canberra, ACT, Australia;
authors.forename: Gus
authors.initials: G
authors.lastname: Koerbin
authors.affiliation: ACT Pathology, Garran, ACT, Australia;
authors.forename: Carmen
authors.initials: C
authors.lastname: Oakman
authors.affiliation: Department of Emergency Medicine and Queensland University of Technology, Brisbane, QLD, Australia;
authors.forename: Louise
authors.initials: L
authors.lastname: Cullen
authors.affiliation: Department of Emergency Medicine, Calvary Hospital, Bruce, ACT, Australia;
authors.forename: Garry J
authors.initials: GJ
authors.lastname: Wilkes
authors.affiliation: Department of Emergency Medicine, The Canberra Hospital, Garran, ACT, Australia.
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Scanlan
authors.affiliation: Queensland University of Technology, Brisbane, QLD, Australia; Department of Cardiology, Royal Brisbane and Women's Hospital, Herston, QLD, Australia;
authors.forename: William
authors.initials: W
authors.lastname: Parsonage
authors.affiliation: ACT Pathology, Garran, ACT, Australia; Australian National University Medical School, Canberra, ACT, Australia; peter.hickman@act.gov.au.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Hickman
mesh_terms: D054058:Acute Coronary Syndrome / Q000097:blood* / Q000175:diagnosis; D015415:Biomarkers / Q000097:blood; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012372:ROC Curve; D012016:Reference Values; D013997:Time Factors; D019210:Troponin I / Q000097:blood*
chemical_list: D015415:Biomarkers; D019210:Troponin I