21 Neutron activation analysis, a method that generates a known amount of radioactivity within a given mass from a defined dose of neutrons, characterizes the elemental composition of the body. Total body potassium counting, a method that measures the natural abundance of radioactive potassium ( 40K) in the body, assesses lean body mass based on the assumption that the potassium content of the FFM is proportional to tissue nitrogen content. 16,17 Total body water can be measured directly by isotope dilution using the stable isotopes of hydrogen ( 2H 2O) or oxygen (H 2 18O) 18 and indirectly by total body electrical conductance 19 or bioelectrical impedance analysis. Air displacement plethysmography is a density technique that measures body composition from body mass and volume within an air-filled chamber. Underwater weighing is a density technique based on the individual’s actual weight and the weight lost while under water. 14,15īody fat and lean body mass can be measured by densitometry or derived from total body water. Waist circumference 12 and waist-for-height 13 may serve as alternative indicators of adiposity because these measure correlate with truncal fat and obesity-related comorbidities. 10,11 Accurate estimates of body fat using anthropometry are difficult to obtain in morbidly overweight children or in children with generalized edema because of altered relationships between body tissue water and fat in these conditions. A method that uses multiple skinfold thickness measurements, such as biceps, triceps, subscapular, and suprailiac sites, may provide a better estimate of body fat and its regional distribution. 9 No single skinfold site is entirely representative of the combined subcutaneous and deep fat stores of the body. 9 The triceps skinfold thickness is most frequently selected as a measure of body fat because it can be compared with reference standards to determine the degree of overweight in children. The upper-arm muscle circumference (or area) serves as a measure of body protein stores because it can be compared with reference standards to determine the degree of muscle wasting in children. A metal tape measure and calibrated skinfold calipers are the only instruments needed. Claudia Conkin, in Pediatric Gastrointestinal and Liver Disease (Fourth Edition), 2011 Methods to Measure Body CompositionĪnthropometry may be used to characterize body composition in the clinical setting.
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