D₃-creatine dilution for the noninvasive measurement of skeletal muscle mass in premature infants

Background: The rate of accrual of muscle mass in neonates has not been assessed. We describe the D₃-creatine (D₃Cr) dilution method, a noninvasive assessment of muscle mass in neonates. Methods: A total of 76 neonates >26-week-old corrected gestational age were enrolled and measured at 2-week intervals while admitted to a neonatal intensive care unit (NICU). Additional measures at 6 and 12–20 months after initial measurement were obtained if available. An enteral dose of 2 mg D₃Cr in 0.5 mL 20% ²H₂O was used to determine muscle mass and total body water (TBW). Results: Muscle mass by the D₃Cr method was strongly associated with TBW and body weight (r = 0.9272, p < 0.0001 and r = 0.9435, p < 0.0001 for all time points and r = 0.6661, p < 0.0001 and r = 0.8634, p < 0.0001, respectively, while in the NICU). Change in muscle mass vs. change in body weight, TBW, and length were also strongly correlated. Conclusions: The D₃Cr dilution method provides a noninvasive assessment of muscle mass accrual in neonates, which has not been previously possible and may be an important new tool for the evaluation of nutritional status and normal growth patterns. Impact: We describe a noninvasive method for the measurement of skeletal muscle mass neonates.At the present time, there is no direct measurement of muscle mass in infants available.The D₃Cr dilution method is a direct and noninvasive measurement of muscle mass.Using a single enteral dose of D₃Cr in ²H₂O followed by urine and saliva samples, rapid and substantial accrual of muscle mass and TBW is assessed.Assessment of muscle mass accrual in premature infants may be a strong indicator of nutritional status.Change in muscle mass is strongly related to change in weight and TBW.