Clinical Utility and Cost Analysis of Cardiac Enzymes Testing in a Community Hospital

Background:

Cardiac Troponins (cTn) are sensitive and specific diagnostic and prognostic markers of myocardial injury. The third Myocardial Infarction (MI) Global Task Force in 2012 de‐emphasized the use of other cardiac biomarkers. Creatine Kinase‐Myocardial fraction (CK‐MB) mass may be used as an alternative to cTn assay, when the latter is not available for MI decision, but other biomarkers including Total Creatine Kinase (CK), CK‐MB activity are largely historical and should no longer be used to diagnose MI. In an era of widespread cTn availability, we report interesting data on current utilization of cardiac enzymes testing in a US suburban hospital.

Methods:

The study is a two‐year (Jan 1, 2011 –Dec 31, 2012) retrospective electronic chart review comprising patients admitted to 326‐bed community hospital in northern Baltimore. All patients who had high‐sensitivity cardiac troponin T (cTnT), CK‐MB mass and CK measured were traced from the Department of Clinical Biochemistry. Exclusion criteria were age <18 years, and a cTnT sample taken in outpatient clinics. Associated medical co‐morbidities of all patients were retrieved with ICD9 codes from Department of Medical Informatics. A measurement level >99^th percentile of upper reference limit for all enzymes was designated as the decision level for the diagnosis of MI. P values <0.05 were considered to indicate statistical significance. Complex analyses were performed using statistical software JMP version 11. We obtained direct cost information from the hospital’s Billing and Finance department for all cardiac enzymes.

Results:

23, 119 test orders were placed for cTnT; with concurrent 23,027 (99.6%) orders for CK‐MB and 22,516 (97.4%) tests for CK. 2,363 (10.2 %) cTnT orders resulted in above decision limit for MI, and 20, 756 cTnT orders (89.8%) were normal. Among elevated cTnT patients, only 66 (2.8%) were found to have type 1 MI (p 0.01). Most patients (65.5%) among elevated cTnT were found to have myocardial necrosis other than coronary artery disease (p <0.001). Similarly, 29% had type 2 MI, 2.5% had type 3 MI, and <0.1% had types 4 and 5 MI. The cost information is presented in the table below. More than a million dollars was spent for testing CK and CK‐MB in two years. The values of these enzymes would be present in cases of rhabdomyolysis. The incidence of rhabdomyolysis was found in 106 (4.5%) cases, but only 6 cases reported cardiac involvement.

Conclusions:

Although testing for CK‐MB and CK along with cTnT for diagnosis of MI adds little clinical utility, these data show an overwhelming number of unnecessary tests still being ordered by physicians in inpatient setting. These reflect the need for change in current practice with optimization of the cardiac enzymes tests in order to reduce the cost. Change in order‐sets for reflex testing for all enzymes, application of better clinical prediction models for ordering cTn, and compliance with latest cardiology guidelines may be helpful.