Creatine Kinase (CK) MB Isoenzyme, Serum
The serial quantitation of serum creatine kinase MB (CKMB) levels, often performed at admission and 8-hours, 16-hours, and 24-hours after admission, has traditionally been used as an aid in the diagnosis of myocardial injury. While CKMB has been replaced by troponin assays in the workup of many patients with acute chest pain, CKMB may be useful if the initial troponin determination is abnormal or if a hospitalized patient has a suspected reinfarction.
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
There are 3 isoenzymes of creatine kinase (CK)-CKBB, CKMM, and CKMB. The primary source of CKMB is myocardium although it is also found in skeletal muscle. CKMB levels increase with myocardial damage. Extreme elevations of CKMB can also be associated with skeletal muscle cell turnover as in polymyositis and to a lesser degree in rhabdomyolysis. It can also be elevated in cases of carbon monoxide poisoning, crush injuries, pulmonary embolism, hypothyroidism, and muscular dystrophy.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Males: <6.7 ng/mL
Females: <3.8 ng/mL
Creatine kinase MB (CKMB) levels can be detected within 3 to 8 hours of the onset of chest pain, peak within 12 to 24 hours, and usually return to baseline levels within 24 to 48 hours.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Creatine kinase MB (CKMB) values, which exceed 50% of the total CK, probably reflect unusual beta-subunit synthesis since the heart muscle rarely exceeds 30% CKMB.
The newer sandwich assays for CKMB have eliminated the confusion seen with older methodologies, but may result in the inability to detect some infrequent contributions to total CK (eg, macro and mitochondrial forms).
In patients receiving treatment with high biotin doses (>5 mg/day) there should be an interval of at least 8 hours between the last biotin administration and the collection of the specimen as biotin interferes with the assay.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
Mair J, Artner-Dworzak E, Dienstl A, et al: Early detection of acute myocardial infarction by measurement of mass concentration of creatine kinase-MB. Am J Cardiol 1991;68:1545-1550