How to interpret creatine kinase level in neuromuscular conditions

Abstract

Creatine kinase (CK) is a screening diagnostic test for suspected neuromuscular disease. It is a sensitive indicator of muscle injury and is preferred to other skeletal muscle enzymes as it is least affected by haemolysis, is readily released in cellular injury and has a relative predominance in skeletal muscle. In a healthy individual the normal range varies between 22 and 200 IU/L (varies with laboratory), although gender and race can influence this range. CK can also be elevated in non-pathological transient situations such as cramps and post-exercise. It can increase up to three times the normal value after strenuous exercise, intramuscular injections, EMG studies and viral infections. Highest level of CK is seen in inflammatory myopathies and in early stages of DMD when patients are still ambulant. Occasionally CK is elevated in asymptomatic or mildly symptomatic children and this creates unwarranted anxiety and diagnostic uncertainties. The need for extensive ancillary investigations and muscle biopsy in clinically normal individuals with elevated CK remains an unresolved issue. This review discusses the diagnostic value of creatine kinase in neuromuscular conditions in children and offers practical advice about how results should be interpreted in different clinical situations.