Prognostic value of cardiac Troponin I after cardiac surgery: comparison with two different assays

Introduction

After adult cardiac surgery, the inhospital prognostic value of cTnI, measured at 20 hours after the end of surgery, has been demonstrated [1]. Various cardiac troponin I (cTnI) assays are available but the lack of standardization renders difficult any comparative study [2]. The aim of this study was therefore to determine cTnI concentration after cardiac surgery using two different assays, and to evaluate their correlation and their respective prognostic values.

Materials and methods

After approval by the local ethic committee and informed consent, 167 consecutive patients undergoing either coronary artery bypass grafting (n = 80) or valve surgery (n = 87) were prospectively studied. The cTnI was measured by an immunoenzymatic method at 10 and 20 hours after the end of surgery (H10 and H20) on two analyzers: RXL^® (Dade Behring) and AxSym^® (Abbott). For each patient, the occurrence of a cardiac event (CE+) was defined as: prolonged low cardiac output (more than 4 hours), Q-wave perioperative myocardial infarction, cardiac death.

Results

A good correlation was found between assay at H10 (r² = 0.81; P < 0.0001) and at H20 (r² = 0.80; P < 0.0001). However, the slopes of the regression equation were different at H10 (3.8) and at H20 (5.6). In the CE+ group, cTnI concentrations were significantly higher at H10 and H20 for both assays (at H20; Dade, 16.3 [28]* vs 3.3 [3.6] cTnI in ng/ml; Abbott, 50.0 [117.9]* vs 9.6 [14.1] cTnI in ng/ml; median [interquartile range], *P < 0.0001, Mann–Whitney test, CE+ vs CE-). Using ROC curve analysis, no difference was found in area under the curve (AUC) at both H10 and H20 between assays, even if at H10 the AUC found with the Dade assay tended to be higher than that of the Abbott assay (0.91 vs 0.80, P = 0.06).

Conclusion

Both assays were found to be well correlated, but the correlation differed with time. cTnI was associated with CE in both assays, with a similar predictive value at H20.