The Measurement of Muscle Mass in Children Using [15N]Creatine

Abstract

Extract: In eight infants and children who had recovered from proteinenergy malnutrition (PEM), muscle mass was estimated by measuring creatine turnover by an isotope dilution technique using [15N]creatine, creatine concentration, and urinary creatinine output. Creatine turnover varied from 1.5 to 2.6% of the muscle creatine pool per day and muscle creatine concentration ranged from 1.7 to 3.9 μg/μg muscle DNA. Muscle mass was between 15% and 37% of total body weight. The results indicate that daily creatinine output is not a reliable indicator of muscle mass in children who have recently recovered from severe PEM. Speculation: Short term fluctuations in the daily creatinine output in young children may be due to variations in muscle creatine concentration since creatine turnover, in the individual subject, remains remarkably constant. The wide variation in the proportion of body weight that is muscle may reflect significant body composition changes in fat, water, and muscle in children who have recovered from severe protein-energy malnutrition.