Comparison of a 3-hour versus a 6-hour sampling-protocol using high-sensitivity cardiac troponin T for rule-out and rule-in of non-STEMI in an unselected emergency department population.

Background: Current European guidelines recommend the use of sensitive or high-sensitivity cardiac troponin assays to reduce the minimal sampling interval from 6 to 3h.
Methods: We compared a 3-hour versus a 6-hour protocol for diagnosis of non-STEMI and used the 99th percentile for rule-out, and relative and absolute concentration changes for rule-in of non-STEMI.
Results: 459 patients with either an NSTE-ACS or elevated hs-cTnT not due to MI and hs-cTnT measurements at 0, 3 and 6h were enrolled. Among the 404 patients excluded due to an incomplete sampling protocol performance was comparable to the 459 patients with a complete sampling protocol (AUC 0.79 vs 0.80, p=ns). In the study group, non-STEMI was diagnosed in 111 cases (24.2%) and elevated hs-cTnT not due to MI was observed in 215 cases (46.8%). For rule-out of non-STEMI, NPVs were 94.9%, 98.7% and 100% on admission, at 3 and 6h with comparable performance at 3 and 6h (AUC 0.782 vs 0.790, p=ns). For rule-in a 3-hour protocol performed as well as a 6-hour protocol, with a significantly (p<0.0001) better performance of absolute (AUC 0.851 vs. 0.845, p=0.740) as compared to relative concentration changes (AUC 0.771 vs. 0.739, p=0.169).
Conclusions: Rule-in and rule-out of non-STEMI may be accomplished comparably effective at 3 or 6h. For rule-in, absolute kinetic changes perform better than relative changes at all time points. ROC-optimal absolute δ-change was 6.95 ng/L at 3h and 8.9 ng/L at 6h.
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