Confirm and monitor therapy after acute myocardial infarction.

Creatine kinase (CK) is an enzyme, found primarily in muscle and brain tissue, which exists as three dimeric isoenzymes: CK-MM (CK-3), CK-MB (CK-2), and CK-BB (CK-1) − built from subunits designated M and B. The CK-MB isoenzyme, which has a molecular mass of approximately 87 kilodaltons, accounts for 5% to 50% of total CK activity in myocardium. In skeletal muscle, by contrast, it normally accounts for ≤1%, CK-MM being the dominant form, though the percentage can be as high as 10% in conditions reflecting skeletal muscle injury and regeneration (eg, severe exercise, muscular dystrophy, polymyositis).¹

CK-MB is one of the most important myocardial markers (in spite of not being altogether cardiac-specific), with well-established roles in confirming acute myocardial infarction (AMI) and in monitoring reperfusion during thrombolytic therapy following AMI.¹

In AMI, plasma CK-MB typically rises some four to six hours after the onset of chest pains, peaks within 12 to 24 hours, and returns to baseline levels within 24 to 48 hours. The pattern of serial CK-MB determinations is more informative than a single determination: one CK-MB measurement, even when taken at an appropriate time, cannot definitively confirm or rule out the occurrence of AMI. High levels might reflect skeletal injury rather than myocardial damage. A value within the reference range might be significant if it represents an increase from the patient's baseline level. (Low baseline levels are sometimes encountered in the elderly.) Accordingly, it has been recommended that CK-MB be measured on admission to the emergency room and at intervals thereafter (eg, at three-hour intervals over a six-hour to nine-hour period in patients with nonspecific electrocardiogram changes;^1,2 or at six-hour to eight-hour intervals over a 24-hour period and more frequently if thrombolytic therapy has been instituted).¹

1. Apple FS, Preese LM. Creatine kinase-MB: Detection of myocardial infarction and monitoring reperfusion. J Clin Immunoassay. 1994; 17:24-29.

2. Gibler WB, Lewis LM, Erb RE, et al. Early detection of acute myocardial infarction in patients presenting with chest pain and nondiagnostic ECGs: serial CK-MB sampling in the emergency department. Ann Emerg Med. 1990 Dec; 19(12):1359-1366. PubMed 2240745

Adams JE 3rd, Schechtman KB, Landt Y, Ladenson JH, Jaffe AS. Comparable detection of acute myocardial infarction by creatine kinase MB isoenzyme and cardiac troponin I. Clin Chem. 1994 Jul; 40(7 Pt 1):1291-1295. PubMed 8013101

Bhayana V, Cohoe S, Leung FY, Jablonsky G, Henderson AR. Diagnostic evaluation of creatine kinase-2 mass and creatine kinase-3 and -2 isoform ratios in early diagnosis of acute myocardial infarction. Clin Chem. 1993 Mar; 39(3):488-495. PubMed 8448862

Bruns DE. Diagnosis of acute myocardial infarction when skeletal muscle damage is present: A caveat regarding use of creatine kinase isoenzymes. Clin Chem. 1989 Apr; 35(4):705. PubMed 2702763

The MB isoenzyme of CK is most commonly elevated in acute myocardial infarction (AMI). In AMI, plasma CK-MB typically rises some four to six hours after the onset of chest pains, peaks within 12 to 24 hours, and returns to baseline levels within 24 to 48 hours. The pattern of serial CK-MB determinations is more informative than a single determination.