[Serum creatine phosphokinase activity: analysis of information provided by different ways of expressing the results]

An experimental model with undernourished rats fed experimental diets containing either imbalanced proteins or low amount of well balanced proteins was used to evaluate the utility of serum CPK activity determination in human malnutrition. Special attention was given on the information provided by four ways of expression of the enzymatic activity. CPK activity was expressed as: 1) Specific activity, 2) Activity per ml serum, 3) Total activity per rat and 4) Total activity per 100 g body weight. Statystical analysis showed: a) Activity expressed per mg serum protein or per ml serum did not agree with the known physiological phenomena induced on muscle by the experimental diets: CPK activity values expressed in these ways are not useful in malnutrition studies. b) Serum total activity of CPK per rat provides a similar information to the creatinin/height index, which is easier to perform. c) Total CPK activity per 100 g body weight demonstrated to be adequate to provide information about muscle mass in rats under controlled experimental conditions. However, it is not possible to use this form of expressing CPK activity in human malnutrition, because it would be also necessary to know: plasma volumen, age, actual body weight, clinical and the nutritional background, etc., of the patient for an accurate interpretation of results.