title: Recovery of spiked troponin I in four routine assays.
abstract: BACKGROUND
  This study aimed to examine the recovery of spiked human cardiac troponin I (cTnI) results measured by four routine assays, and investigate possible interference from microclots.
  
  
  METHODS
  457 consecutive samples with cTnI concentration below limit of quantitation (12 ng/L), declared by the Vitros TnI ES assay (reference assay), were measured on Beckman Coulter Accu TnI+3, Siemens TnI-Ultra and Roche TnI STAT assays. These samples were enriched with native full-length cTnI to a concentration of 100 ng/L and retested. A post-spiking result that exceeded the critical difference at a predefined probability of 0.0005 of the target concentration (the median post-spiking result for each individual assay) was considered as outlier. To determine whether microclots were a significant cause of critically discrepant outlier results, a separate 50 samples were centrifuged twice between two post-spiking measurements using the Vitros TnI ES assay.
  
  
  RESULTS
  The median recovery of the enriched cTnI was highest with the Roche assay (271 ng/L) and lowest with the Vitros assay (29 ng/L). The Vitros assay had the highest percentage of results that exceeded the critical difference (49%), followed by the Siemens (38%), Roche (18%) and Beckman Coulter (7%) assays. None of the 50 additional samples produced a critically lower cTnI result after re-centrifugation.
  
  
  CONCLUSIONS
  Our findings underscored the variability of cTnI assays in measuring native cTnI. The lack of cTnI results that became significantly lower after re-centrifugation suggested that microclots are unlikely to be a major cause of the outlier results.
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Tze Ping
authors.initials: TP
authors.lastname: Loh
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Xiong Chang
authors.initials: XC
authors.lastname: Lim
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Karize
authors.initials: K
authors.lastname: Kieu
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Haressh
authors.initials: H
authors.lastname: Sajiir
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Siew Fong
authors.initials: SF
authors.lastname: Neo
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Wan Ling
authors.initials: WL
authors.lastname: Cheng
authors.affiliation: Department of Laboratory Medicine, National University Hospital, Singapore, Singapore.
authors.forename: Sunil Kumar
authors.initials: SK
authors.lastname: Sethi
mesh_terms: D001681:Biological Assay / Q000379:methods* / Q000592:standards; D006801:Humans; D012680:Sensitivity and Specificity; D019210:Troponin I / Q000097:blood*
chemical_list: D019210:Troponin I
keywords: cardiovascular diseases; clinical chemistry; immunoassay; troponin