title: Sensitive troponin assay and the classification of myocardial infarction.
abstract: BACKGROUND
  Lowering the diagnostic threshold for troponin is controversial because it may disproportionately increase the diagnosis of myocardial infarction in patients without acute coronary syndrome. We assessed the impact of lowering the diagnostic threshold of troponin on the incidence, management, and outcome of patients with type 2 myocardial infarction or myocardial injury.
  
  
  METHODS
  Consecutive patients with elevated plasma troponin I concentrations (≥50 ng/L; n = 2929) were classified with type 1 (50%) myocardial infarction, type 2 myocardial infarction or myocardial injury (48%), and type 3 to 5 myocardial infarction (2%) before and after lowering the diagnostic threshold from 200 to 50 ng/L with a sensitive assay. Event-free survival from death and recurrent myocardial infarction was recorded at 1 year.
  
  
  RESULTS
  Lowering the threshold increased the diagnosis of type 2 myocardial infarction or myocardial injury more than type 1 myocardial infarction (672 vs 257 additional patients, P < .001). Patients with myocardial injury or type 2 myocardial infarction were at higher risk of death compared with those with type 1 myocardial infarction (37% vs 16%; relative risk [RR], 2.31; 95% confidence interval [CI], 1.98-2.69) but had fewer recurrent myocardial infarctions (4% vs 12%; RR, 0.35; 95% CI, 0.26-0.49). In patients with troponin concentrations 50 to 199 ng/L, lowering the diagnostic threshold was associated with increased healthcare resource use (P < .05) that reduced recurrent myocardial infarction and death for patients with type 1 myocardial infarction (31% vs 20%; RR, 0.64; 95% CI, 0.41-0.99), but not type 2 myocardial infarction or myocardial injury (36% vs 33%; RR, 0.93; 95% CI, 0.75-1.15).
  
  
  CONCLUSIONS
  After implementation of a sensitive troponin assay, the incidence of type 2 myocardial infarction or myocardial injury disproportionately increased and is now as frequent as type 1 myocardial infarction. Outcomes of patients with type 2 myocardial infarction or myocardial injury are poor and do not seem to be modifiable after reclassification despite substantial increases in healthcare resource use.
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Anoop S V
authors.initials: AS
authors.lastname: Shah
authors.affiliation: Centre for Population Health Sciences, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: McAllister
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Rosamund
authors.initials: R
authors.lastname: Mills
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Kuan Ken
authors.initials: KK
authors.lastname: Lee
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Antonia M D
authors.initials: AM
authors.lastname: Churchhouse
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Fleming
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Layden
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Atul
authors.initials: A
authors.lastname: Anand
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Omar
authors.initials: O
authors.lastname: Fersia
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Nikhil V
authors.initials: NV
authors.lastname: Joshi
authors.affiliation: Department of Clinical Biochemistry, Royal Infirmary of Edinburgh, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Walker
authors.affiliation: Mayo Clinic, Rochester, Minn.
authors.forename: Allan S
authors.initials: AS
authors.lastname: Jaffe
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: Keith A A
authors.initials: KA
authors.lastname: Fox
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom.
authors.forename: David E
authors.initials: DE
authors.lastname: Newby
authors.affiliation: BHF Centre for Cardiovascular Science, Edinburgh University, Edinburgh, United Kingdom. Electronic address: nick.mills@ed.ac.uk.
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Mills
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D015994:Incidence; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000145:classification* / Q000401:mortality / Q000628:therapy; D019210:Troponin I / Q000097:blood*
chemical_list: D019210:Troponin I
keywords: Myocardial infarction; Outcomes; Troponin; Type 2