Body Composition and Plasma Creatine Kinase Activity

Abstract

SUMMARY.Plasma creatine kinase (CK) activity and lean body mass (LBM) (by anthropometry) were measured in 120 women (20-82 years) and 70 men (20-82 years). Plasma CK activity and LBM was higher in men than in women. In men plasma CK activity was significantly correlated (product moment correlation coefficient) with LBM and negatively with age. In women plasma CK activity was significantly correlated with age. Partial correlation coefficient calculation showed a significant correlation between plasma CK and LBM both in men and in women. We conclude that in healthy subjects the plasma CK activity is related to LBM, but the LBM is not a major determinant of plasma activity in healthy subjects.Measurement of creatine kinase (CK), adenosine triphosphate: creatine phosphotransferase EC 2.7.3.2, an enzyme present in muscle, heart and brain, is useful in the diagnosis of acute myocardial infarction, in muscle disorders such as Duchenne muscular dystrophyI and in the study of exercise stress. However, the reference range for CK is wide and the specificity of CK in the detection of muscular dystrophy is 'low and attempts have been made to narrow the reference range. Many factors contribute to the wide reference range including age,2 hormone status," race" and sex", It is well known that men have a higher CK than women and most laboratories use sex-related reference ranges. It has also been suggested plasma CK is related to muscle mass?: 7 although some disagree." We have, therefore, studied the relationship between LBM and CK in a large group of subjects. Materials and methodsChinese individuals, living in a government housing estate, were studied. Each week, over several months, we collected blood samples from a group of to to 25 fasted individuals after anthropometric measurements--weight, height, and skinfold thickness measurement at biceps, triceps, subscapular, and suprailiac sites with a Langer skinfold caliper. Blood was collected into lithium heparin tubes, kept at 4°C, and centrifuged within 2 h. Plasma was separated and stored at -700C until analysis. We assayed CK on a centrifugal analyser (Encore, Baker Instruments, Allentown, PA, USA) by the IFCC recommended method. For CK activities of 62 and 237 UIL the withinbatch SD were 1·0 (CY 1·6%) and 7·1 UIL (CV 3,0%) and the between-batch SD were 1·4 (CY 2·2%) and 10·2 UIL (CY 4,3%), respectively. Lean body mass (LBM) was calculated from the sum of four skinfold thickness usinẽ quations described by Durnin and Wormsley. We also calculated the body mass index (BMI) (weight/heighr'). After excluding men and women whose log CK values exceeded the mean±3 SD for each sex, there were 120 women (20-82 years) and 70 men (20-82 years) in the study.Differences between groups were evaluated by Student's r-test. Log transformation of data was used to normalise distribution of CK. Product moment correlation coefficients and partial correlation coefficients were calculated according to Steel and Tome. 10

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