Proposed New Cutoff Value for Troponin in the Diagnosis of Acute Myocardial Infarction (AMI) in Patients with Congestive Heart Failure (CHF) and/or End Stage Renal Disease (ESRD)

Abstract

Abstract Introduction/Objective In a recent publication, we assessed the efficacy of two serum biomarkers for AMI, cardiac Troponin I (cTnI) and creatine kinase-MB (CK-MB), for patients presenting to our emergency department (ED) with acute chest pain. We found that two conditions, CHF and ESRD in 85 patients, caused a significant number of false positive results that resulted in lowering the specificity and positive predictive value of both tests, which were already reduced by the low prevalence of AMI in our patient population. Removal of these patients resulted in significant increases in the two latter parameters. In this study, we focus on cTnI to determine if changing the cutoff value can increase the sensitivity and specificity of diagnosing acute MI in patients with CHF and ESRD. Methods/Case Report A cohort of 380 patients who presented with acute chest pain in the ED and worked up for acute MI were included, 85 of whom had CHF and/or ESRD. A total of 47 patients (15.4% prevalence) were definitively diagnosed with AMI. An initial serum cTnI sample was collected for each patient. Specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) were then compared using the routine cutoff cTnI value (0.05 ng/mL) and the higher cutoff of 0.2 ng/mL. Results (if a Case Study enter NA) Using the original cutoff of 0.05 ng/mL for cTnI in the patients with CHF or ESRD, the sensitivity and NPV were both 100%, while the specificity and PPV were low at 40.3% and 23%, respectively. Interestingly, when the cutoff was raised from 0.05 to 0.2 ng/mL, the sensitivity decreased by about 8% to 92.3 (12 out of 13 patients with AMI), and the specificity increased almost two-fold to 76.4%. The PPV increased to 40.4% and NPV was 98.2%. These values are comparable with the sensitivity, specificity, PPV and NPV of the total population at 85.3%, 82.4%, 38.7% and 97.7%, respectively. Conclusion The original cutoff value for cTnI in patients with ESRD and CHF produces a very low specificity and PPV. The results of this study suggest that an acceptable cutoff for cTnI to rule-out AMI patients who have CHF and or ESRD is 0.2 ng/mL which is four times higher than the original, but has comparable specificity, sensitivity, PPV and PPV to the total patient population. We note that this study must be regarded as a pilot study since the numbers of patients are small. We recommend a larger study to determine the validity of these conclusions.