Cardiac Troponin I A MarkerWithHighSpecificity forCardiac Injury

Background. Levels ofMBCK canbeincreased inpatients withskeletal muscleinjury orrenal failure intheabsence ofmyocardial injury, causing diagnostic confusion. Thisstudy was designed todetermine whether measurement ofcardiac troponin I(cTnI), a myocardial regulatory protein withcomparable sensitivity toMBCK,hassufficient specificity toclarify theetiology ofMBCK elevations inpatients with acute orchronic skeletal muscledisease orrenalfailure. Methods andResults. Ofthepatients (n=215) studied, 37hadacuteskeletal muscleinjury, 10had chronic muscledisease, nineweremarathon runners,and159were chronic dialysis patients. Patients were evaluated clinically, byECG,andbytwo-dimensional echocardiography. Totalcreatine kinase (normal, <170IU/L) was determined spectrophotometrically, andcTnI(normal, <3.1ng/mL)and MBCK (normal, <6.7ng/mL) weredetermined withspecific monoclonal antibodies. Valuesabovethe upperreference limit wereconsidered "elevated." Elevations oftotal creatine kinase werecommon,and elevations ofMBCK occurred in59%oofpatients withacutemuscleinjury, 78%ofpatients withchronic muscledisease andmarathon runners,and3.8%o ofpatients withchronic renalfailure. Someofthe patients werecritically ill; fivepatients werefoundtohavehadmyocardial infarctions andone hada myocardial contusion. cTnIwas elevated onlyinthese patients. Conclusions. Elevations ofcTnIarehighly specific formyocardial injury. UseofcTnIshould facilitate distinguishing whether elevations ofMBCK areduetomyocardial orskeletal muscleinjury. (Circulation 1993;88:101-106)