Early Troponin I in critical illness and its association with hospital mortality: a cohort study: Early Troponin I in ICU and hospital mortality
Background: Troponin I (TnI) is frequently elevated in critical illness, but its interpretation is unclear. Our primary objectives were to evaluate whether TnI is associated with hospital mortality, and if this association persists after adjusting for potential confounders. We also aimed to ascertain whether addition of TnI to the APACHE II risk prediction model improves its performance in general ICU populations.
Methods: We performed an observational cohort study, with independent derivation and validation cohorts in two general level 3 ICU departments in the UK.
Derivation cohort: 4.5 year cohort (2010-2014) of general ICU index admissions (n=1,349).
Validation cohort: Secondary analysis of prospective study dataset (2010) (n=145). The primary exposure was plasma TnI concentration taken within 24 hours of ICU admission. The primary outcome was hospital mortality. We performed multivariate regression adjusting for components of the APACHE II model. We derived the risk prediction score from the multivariable model with TnI.
Results: Hospital mortality was 37.3% (n=242) for patients with detectable TnI, compared with 14.6% (n=102) for patients without detectable TnI. There was a significant univariate association between TnI and hospital mortality (OR per doubling TnI 1.16, 95%CI 1.13, 1.20, p<0.001). This persisted after adjustment for APACHE II model components (OR TnI 1.05, 95%CI 1.01, 1.09, p=0.003). TnI correlated most strongly with the Acute Physiological Score (APS) component of APACHE II (r=0.39). Addition of TnI to the APACHE II model did not improve discrimination (APACHE II c-index 0.835 (95%CI 0.811, 0.858); APACHE II+TnI c-index 0.837 (95%CI 0.813, 0.860), p=0.330), or improve other measures of model performance.
Conclusions: TnI is an independent predictor of hospital mortality, and correlates most highly with the APS component of APACHE II. It does not improve risk prediction. We would not advocate the adoption of routine troponin analysis on admission to ICU, and recommend that troponin is measured only if clinically indicated.