Serum creatine kinase: requesting and interpreting results.

Creatine kinase is an intracellular enzyme found abundantly in skeletal muscle, myocardium and brain. It is well known as a biomarker that increases following skeletal muscle damage and doctors instinctively associate it with myopathies. Serum creatine kinase is undoubtedly often raised in many myopathies and the extent of increase may provide a clue to the myopathic culprit. However, in other myopathies, it may be normal or only marginally raised, and rarely it is normal when the underlying pathology suggests that it should be very raised. Creatine kinase can also be raised in neurogenic disorders, and it can help in the investigation of some neurological disorders that are unrelated to neuromuscular disease. Finally, it may be discovered to be mysteriously elevated without a clear clinical correlate. Here, we examine each of these conundrums, beginning with the clinical problem at hand.