Macro CK Isoenzyme

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Subject: Macro CK Isoenzyme

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Definition

  • This isoenzyme is a high molecular mass complex of a CK isoenzyme and immunoglobulin, most often CK-BB and monoclonal IgG and a kappa light chain. Macro CK type 2 is an oligomeric mitochondrial CK complex that migrates cathodically or close to CK-MM. It is found primarily in adults who are severely ill with malignancies or liver disease, or in children who have myocardial disease. It occurs transiently in about 1% of hospitalized patients and indicates a poor prognosis, except in children.

Use

  • Macroenzymes should be suspected when enzyme levels are persistently raised with relatively constant levels, and there is no obvious clinical explanation or other laboratory abnormality.

Interpretation

  • The clinical relevance of macro CK type 1 is not clearly established. It is not associated with a particular type of disease and has been observed in patients with various diseases, as well as in apparently healthy individuals. There are several reported disease associations, including hypothyroidism, neoplasia, autoimmune disease, myositis, and cardiovascular disease. The last two have the strongest reported associations and may support the diagnosis of an autoimmune process, but this may in part be explained by a higher frequency of requests for CK levels in these groups of patients. Myositis, including autoimmune myositis, polymyositis, malignancy-associated dermatomyositis, and drug-induced myositis, has been diagnosed in >50% of the patients with macro CK type.

  • Atypical macro isoenzyme is found primarily in adults who are severely ill with malignancies or liver disease or in children who have myocardial disease. It occurs transiently in about 1% of hospitalized patients and indicates a poor prognosis, except in children.

Limitations

  • Atypical macro isoenzyme may cause falsely high or low CK-MB results (depending on type of assay), resulting in an incorrect diagnosis of myocardial infarction (MI) or delayed recognition of an actual MI. The atypical macro isoenzyme is discovered in <2% of all CK isoenzyme electrophoresis studies.

 
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