Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (861 page)

   Detection of macroforms of creatine kinase (CK)

   Diagnosing skeletal muscle disease, in conjunction with aldolase

   CK isoenzymes are not widely used in clinical practice today due to the use of troponin and CK-MB mass assays but may be useful in differential diagnosis when CK elevated as well

   
The CK-BB isozyme is rarely encountered clinically.

   Interpretation

Increased In

   Malignant hyperthermia, uremia, brain infarction or anoxia, Reyes syndrome, necrosis of the intestine, various metastatic neoplasms (especially prostate), biliary atresia

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.