Introduction: The diagnosis of non-ST elevated myocardial infarction (NSTEMI) depends on a combination of history, ECG and cardiac biomarkers. Many hospitals continue to automatically order less sensitive and specific biomarkers such as Creatine Kinase (CK) alongside cardiac Troponin (cTn) as part of an extended panel of bloodwork for work-up of patients with suspected NSTEMI. Methods: We undertook a systematic review to assess the usefulness of CK measurements in addition to cTnI in NSTEMI diagnosis. Medline, EMBASE and Cochrane databases were searched from 1995 until May 31, 2018. We added additional articles after reviewing the reference list of pertinent articles and consulting experts. A total of 1123 papers were screened, of which 8 were included in the final analysis. These papers all compared CK and troponin (TnI) testing in the diagnosis of NSTEMI. Results: Of the 8 papers included in the analysis none showed CK having a greater sensitivity or specificity than the TnI assays. Furthermore, no paper originally published evidence of CK diagnosing NSTEMI when Troponin was negative. One author, when contacted, described 10% of patients diagnosed with NSTEMI as having discordant data (eg. +CK, -Troponin). However, the outcome data such as angiography and echocardiography were not available for these patients, making definitive diagnosis unclear. Conclusion: Troponin has consistently shown to have greater sensitivity and specificity than CK in the diagnosis of NSTEMI with CK adding no improvements in diagnosis. We believe CK should not be used in the emergency department work-up for NSTEMI diagnosis.

Introduction: Creatine kinase (CK) measurement, despite not being recommended for the diagnosis of a Non-ST Elevation Myocardial Infarction (NSTEMI) is still routinely performed in the emergency department (ED) for the workup of NSTEMI. The diagnostic utility of CK among ED patients with suspected NSTEMI is still not well understood. The objectives of this study were to assess: the additional value of CK in NSTEMI diagnosis and the correlation between the highest CK/TNI values and ejection fraction (EF) on follow-up echocardiography among patients with suspected NSTEMI. Methods: This was a prospective cohort study conducted at the Civic and General Campuses of The Ottawa Hospital from March 2014 to March 2016. We enrolled adults (18 years) for whom troponin (TNI) and CK were ordered for chest pain or non-chest pain symptoms within the past 24 hours concerning for NSTEMI and excluded those with suspected ST-Elevation Myocardial Infarction (STEMI). Primary outcome was a 30-day NSTEMI adjudicated by two blinded physicians. Demographics, medical history, and ED CK/TNI values were collected. We used descriptive statistics and report test diagnostic characteristics. Results: Of the 1,663 patients enrolled, 84 patients (5.1%) suffered NSTEMI. The sensitivity and specificity of CK was 30.9% (95%CI 21.1, 40.8) and 91.4% (95%CI 90.0, 92.8) respectively. The sensitivity and specificity of troponin was 96.4% (95%CI 92.4, 100) and 88.1% (95%CI 86.5, 89.7) respectively. Among 3 (0.2%) patients with missed NSTEMI diagnosis with TNI, CK measurements did not add value. The mean CK values were not significantly different between those with normal and abnormal EF on follow-up (132.4 U/L and 146.3 U/L respectively; p=0.44), whereas the mean TNI values were significantly different (0.5 µg/L and 1.3 µg/L respectively; p=0.046). Conclusion: CK measurements neither provide any additional value in the work-up of NSTEMI in the ED nor correlate with EF on follow-up. Discontinuing routine CK measurements would reduce overall costs and improve resource utilization in the ED, and streamline the management of patients in the ED with chest pain.