title: Sources of variability in measurements of cardiac troponin T in a community-based sample: the atherosclerosis risk in communities study.
abstract: BACKGROUND
  Application of cardiac troponin T (cTnT) as a marker of myocyte damage requires knowledge of its measurement variability. Using a highly sensitive assay for measurement, we evaluated the long-term storage stability of plasma cTnT at -70 °C and the sources of cTnT variability.
  
  
  METHODS
  Samples from the Atherosclerosis Risk in Communities study collected in 1996-1998 and 2005-2006 were assayed centrally to quantify variability in cTnT attributable to processing (replicates from same blood draw, n = 87), laboratory (replicates after freeze thaw, n = 29), short-term (n = 40) and long-term biological variation (repeat visit, n = 38), and degradation in frozen storage (n = 7677).
  
  
  RESULTS
  Approximately 30% of this population-based cohort had cTnT concentrations below the detection limit (3 ng/L). Reliability coefficients for all paired comparisons exceeded 0.93 except for samples drawn 8 years apart (r = 0.36). Sources of cTnT variation (as CVs) were: laboratory, 2.1% and 11.2% in those with and without heart failure, respectively; processing, 18.3%; biological, 16.6% at 6 weeks and 48.4% at 8 years. The reference change value at 6 weeks (68.5%) indicated that 4 samples are needed to determine a homeostatic set point within ±25%. The estimated cTnT degradation rate over the first year in long-term frozen storage was 0.36 ng/L per year.
  
  
  CONCLUSIONS
  cTnT was detectable in approximately 70% of community-dwelling middle-aged study participants and stable in -70 °C storage. The variability in cTnT attributable to 1 freeze-thaw cycle is of small magnitude. The observed high laboratory and intraindividual (biological) reliability of cTnT support its use for population-based research, and in clinical settings that rely on classification and serial measurements.
authors.affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Agarwal
authors.forename: Christy L
authors.initials: CL
authors.lastname: Avery
authors.forename: Christie M
authors.initials: CM
authors.lastname: Ballantyne
authors.forename: Diane
authors.initials: D
authors.lastname: Catellier
authors.forename: Vijay
authors.initials: V
authors.lastname: Nambi
authors.forename: Justin
authors.initials: J
authors.lastname: Saunders
authors.forename: A Richey
authors.initials: AR
authors.lastname: Sharrett
authors.forename: Josef
authors.initials: J
authors.lastname: Coresh
authors.forename: Gerardo
authors.initials: G
authors.lastname: Heiss
authors.forename: Ron C
authors.initials: RC
authors.lastname: Hoogeveen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D050197:Atherosclerosis / Q000097:blood / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D001800:Blood Specimen Collection; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012111:Residence Characteristics; D018570:Risk Assessment; D013696:Temperature; D013997:Time Factors; D020107:Troponin T / Q000097:blood*
chemical_list: D015415:Biomarkers; D020107:Troponin T