CREATINE KINASE (CK) - plasma or serum

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Specimen: 5 mL blood in lithium heparin or plain tube.

Method: Spectrophotometry.

Reference Interval: Influenced by gender and method; local laboratory reference intervals should be ascertained. Typically:

Neonate:		70-380 U/L
Adult:	male:	60-220 U/L
	female	30-180 U/L

Application: A sensitive, but not specific, test for the diagnosis and monitoring of myocardial infarction; CKMB with CKMB/CK ratio is more specific, but has been superseded by cardiac troponin T or I. Levels of CK are increased in diseases affecting skeletal muscle. It can be used to detect carrier status for Duchenne muscular dystrophy, although not all carriers have increased levels.

Interpretation: Elevation of CK, CKMB and CKMB as a percentage of CK, indicates a myocardial origin of CK. CK levels may also be increased with skeletal muscle injury eg after intramuscular injection or excessive exercise, in myositis, myopathy, rhabdomyolysis or hypothyroidism. Elevation of no pathological significance is seen in patients with a “macro-CK” – a complex of CK with an immunoglobulin. Isoenzyme studies may be useful in investigating increased CK activities of uncertain cause.

Reference: Bais R et al. Pathology 1988; 20: 367-372.

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