This lab test panel includes Total CK (or CPK) and relative percentage of BB (CK-1), MB (CK-2), and MM (CK-3); the percentage of macro CK, if present.
The CK or CPK isoenzyme test is used to diagnose myocardial infarction (MI). Three fractions normally may be found, each an isoenzyme:
• MM is found in normal serum.
• MB is the myocardial fraction associated with MI and occurs in certain other states. MB can be used in estimation of infarct size.
MB increases have been reported with entities that cause damage to the myocardium, such as myocarditis, some instances of cardiomyopathy, and with extensive rhabdomyolysis, Duchenne muscular dystrophy, malignant hyperthermia, polymyositis, dermatomyositis, mixed connective tissue disease, myoglobinemia, Rocky Mountain spotted fever, Reye syndrome, and rarely in rheumatoid arthritis with high titer RF.2 CK-MB does not generally abruptly rise and fall in such nonacute MI settings, as it does in acute myocardial infarct (AMI).
• BB is rarely present. BB has been described as a marker for adenocarcinoma of the prostate, breast, ovary, colon, adenocarcinomas of gastrointestinal tract, and for small cell anaplastic carcinoma of lung. BB has been reported with severe shock and/or hypothermia, infarction of bowel,3 brain injury, stroke, as a genetic marker in some families with malignant pyrexia, and with MB in alcoholic myopathy.
Exercise, intramuscular injections, myxedema, grand mal seizures, prior trauma or surgery, and acute MI very early or late lead to the combination of increased total CK but usually normal CK-MB. Increased CK-MB has been described in marathon runners without MI.4 CK isoenzyme analysis is not usually practical when the total CK is very low, although in elderly people with low muscle mass, the use of sensitive mass concentration assays may be useful. A single CK isoenzyme examination may be misleading.