Is fat mass a better predictor of 6-month survival than muscle mass among African children aged 6-59 months with severe pneumonia?

Background Pneumonia remains the leading cause of mortality among children under 5 years. Poor nutritional status increases pneumonia mortality. Nutritional status assessed by anthropometry alone does not provide information on which body composition element predicts survival. Body composition proxy measures including arm-fat-area (AFA), arm-muscle-area (AMA), and arm-muscle-circumference (AMC) could be useful predictors. Objective To compare the ability of fat and muscle mass indices to predict 6-month survival among children with severe pneumonia. Methods This prospective cohort study was nested in the COAST-Nutrition trial (ISRCTN10829073, 06/06/2018) conducted between June 2020 and October 2022 in Uganda and Kenya. We included children aged 6-59 months hospitalized for severe pneumonia with hypoxemia. Children with severe malnutrition, known chronic lung or cardiac diseases were excluded. Anthropometry and clinical status were assessed at enrolment and at follow-up to day 180. We examined Receiver Operator Characteristic (ROC) curves of fat and muscle mass indices with 6-month survival as the outcome, and compared the areas under the curve (AUCs) using chi-square tests. Cox survival analysis models assessed time-to-mortality. Results We included 369 participants. The median age was 15-months (IQR 9, 26), and 59.4% (219/369) of participants were male. The baseline measurements were: median MUAC 15.0 cm (IQR 14.0,16.0); arm-fat-area 5.6cm(2) (IQR 4.7, 6.8); arm-muscle-area 11.4cm(2) (IQR 10.0, 12.7); and arm-muscle-circumference 12.2 cm (IQR 11.5, 12.9). Sixteen (4.3%) participants died and 4 (1.1%) were lost-to-follow-up. The AUC for Arm-Fat-Area was not significantly higher than that for Arm-Muscle-Area and Arm-Muscle-Circumference [AUC 0.77 (95%CI 0.64-0.90) vs. 0.61 (95%CI 0.48-0.74), p = 0.09 and 0.63 (95%CI 0.51-0.75), p = 0.16 respectively], but was not statistically different from MUAC (AUC 0.73 (95%CI 0.62-0.85), p = 0.47). Increase in Arm-Fat-Area and Arm-Muscle-Circumference significantly improved survival [aHR 0.40 (95%CI 0.24-0.64), p = < 0.01 and 0.59 (95%CI 0.36-1.06), p = 0.03 respectively]. Survival prediction using Arm-Fat-Area was not statistically different from that of MUAC (p = 0.54). Conclusions Muscle mass did not predict 6-month survival better than fat mass in children with severe pneumonia. Fat mass appears to be a better predictor. Effects of fat and muscle could be considered for prognosis and targeted interventions.