Racial differences in serum creatine kinase levels

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Total creatine kinase was measured in serum samples obtained from 307 asymptomatic healthy subjects, 112 men and 195 women, during screening visits to the Yale University Hypertension Clinic or the Yale-New Haven Hospital Primary Care Center or during pre-employment physical examinations at the Yale-New Haven Hospital Personnel Health Clinic. The group consisted of 147 blacks, 132 whites, and 28 Hispanics. Blood pressure was measured in all patients, and weight, height, and serum potassium and creatinine levels were determined in most. Any subject who had engaged in any vigorous exercise in the 12 hours prior to the visit was excluded. The mean total creatine kinase level for black men was 146.5 ± 136.9 units/liter (median, 108 units/liter), the mean level for white men was 60.8 ± 26.1 units/liter (median, 51 units/liter), and the mean level for Hispanic men was 84.5 ± 70.6 units/liter (median, 57 units/liter). The mean level for black women was 66.4 ± 50.0 units/liter (median, 53 units/liter), the mean level for white women was 37.0 ± 18.2 units/liter (median, 32 units/liter), and the mean level for Hispanic women was 41.5 ± 36.0 units/liter (median, 30 units/liter). Using the testing laboratory's normal values for total creatine kinase (8 to 80 units/liter for men and 5 to 50 units/liter for women), 37 black men (64.9 percent) and 49 black women (54.4 percent) had abnormal values for total creatine kinase. Although sex, race, diastolic blood pressure, serum creatinine level, and presence of hypertension correlated significantly with total creatine kinase levels in the entire population, only sex did so in blacks. Multivariate analysis using linear regression techniques clearly demonstrated that sex and race were the only variables that independently predicted the total creatine kinase level. These findings show that healthy asymptomatic blacks have higher total creatine kinase levels than whites or Hispanics, with the majority having values in the abnormal range. Thus, different normal values should be used for blacks, just as they are for men and women, and elevated total creatine kinase levels should be interpreted with considerable caution.