Novel Approach: Measurement of Partial Body Potassium in the Arm in Children

We introduce a novel measurement of partial body potassium in the arm (PBKArm) using a shielded, four NaI gamma ray detector system that surrounds the arm. The K measurement in the arm is directly related to the skeletal muscle (SM) mass since the amount of K in the skin and bone contributing to the total counts is small. Two cohorts (males and females) consisting of 26 pediatric subjects (7 to 19 yrs) and 50 adults (19 to 87 yrs) were measured for PBKArm, total body potassium (TBK), and lean soft tissue (LST) by DXA in the dominant arm. PBKArm in children shows a systematic increase with age although rate of increase with age differed between males and females, 0.3 g/yr and 0.06 g/yr, respectively. These increases are directly attributable to the increase in the arm SM. TBK, which obscures the arm SM, also showed a similar increase with age, although sex difference was less pronounced. In adults, PBKArm showed a decline with increasing age at the rate of 0.12 g/yr for both sexes, similar to the trends observed with TBK. In addition, PBKArm values were systematically higher for males than for females, which is due to the higher SM content in males than in females. In children, PBKArm was also strongly correlated with DXA arm LST for males (r2 = 0.90, p<9E-8) and females (r2 = 0.65, p<0.003). Whereas in adults, lower correlations were observed (male: r2 = 0.41, p<0.007, females: r2 = 0.08, p<0.1). In summary, we demonstrate the feasibility of measuring PBKArm in children, thus providing a direct measure of the SM compartment. PBKArm constitutes a new tool to the fundamental body composition measures. Support: NIH Grant PO1-DK 42618.