CREATINE phosphokinase (CPK) is an enzyme abundantly present in skeletal and cardiac muscle cells. It catalyzes the phosphorylation of muscle creatine, a reversible reaction requiring adenosine triphosphate (ATP):
In 1959 Ebashi et al first utilized the measurement of this enzyme as a diagnostic aid.1 They determined the serum creatine phosphokinase (SCPK) in patients with muscular disorders and found abnormal elevations in a large percentage of patients with progressive muscular dystrophy of the Duchenne type. Other investigators have since confirmed these findings2-4 and in addition have enlarged the diagnostic possibilities by finding abnormally high SCPK values in other disorders affecting muscle tissue, such as dermatomyositis3,4 hypothyroidism,5 following cardiac surgery,6 and during acute myocardial infarction.7-10
Since CPK is so heavily concentrated in muscle, as opposed to other tissues,11 it possesses a potentially high degree of diagnostic specificity, in contradistinction to the ubiquitous transaminases and dehydrogenases. Therefore, it is surprising that