Relationship of Ethnic Origin, Gender, and Age to Blood Creatine Kinase Levels

BACKGROUND: Creatine kinase is expressed at high levels in muscle, where it plays a central role in energy metabolism. Highly elevated creatine kinase levels in blood may indicate muscle trauma or disease. However, it is known that baseline creatine kinase levels are higher in African Americans than in whites and that they are higher in men than in women. This analysis explores the relationship of ethnic origin, gender, and age to baseline blood creatine kinase levels in a large group of adults with hypercholesterolemia. METHODS: Data from the screening phases of 4 North American trials of statins, which included large numbers of specific racial/ethnic populations, were combined for analysis. The pooled population (N = 11,346) included 2760 African Americans, 3301 whites, 2930 Hispanics, and 2355 South Asians. RESULTS: Creatine kinase levels varied according to ethnic origin, gender, and age. African American participants had higher median creatine kinase levels than did individuals of the 3 other ethnicities. Within each ethnic group, men had higher median creatine kinase levels than women: African Americans, 135 versus 73 U/L; whites, 64 versus 42 U/L; Hispanics, 69 versus 48 U/L; and South Asians, 74 versus 50 U/ L. An age-dependent decrease in creatine kinase levels was noted among men, but no such trend was seen among women. The median creatine kinase levels for younger African American men exceeded the standard upper limit of normal. CONCLUSION: Physicians should use caution when interpreting creatine kinase levels that seem elevated, particularly when treating African American patients and younger men. (C) 2009 Published by Elsevier Inc. The American Journal of Medicine (2009) 122, 73-78