Development of a growth reference for the mid-upper arm circumference (MUAC) as an anthropometric indicator of protein status in marginally nourished populations.

Abstract

This dissertation focuses on the development of a marker of protein status to identify children with severe negative energy balance and protein deficiency. Such a tool would have considerable value in epidemiological studies since muscle mass is an important indicator of protein-energy malnutrition (PEM). While biochemical measures are available to precisely measure muscle protein status, anthropometry provides an inexpensive practical means for the assessment of muscle mass in developing countries where severe PEM is prevalent. This dissertation addresses the utility of the anthropometric measurement of the mid-upper arm circumference (MUAC) as an indicator of muscle mass for the evaluation of protein status in marginally nourished populations. A standardized reference for MUAC has been developed which takes into account the observed variations in MUAC by age and gender to obtain a biologically meaningful assessment of protein status. Using data from the Second National Health and Nutrition Examination Survey (NHANES II), several polynomial regression models were constructed to compute MUAC z-scores. Poor correspondence between the MUAC z-scores and other anthropometric indices, e.g., WFA, HFA and WFH, was noted which suggests that distinct biological processes and manifestations of malnutrition may be detected by different anthropometric measures. In addition, both age and gender are important covariates in the classification of malnutrition. The association of clinical vitamin A deficiency (VAD) with standardized MUAC as an index of protein deficiency among children was assessed. The MUAC z-score was found to be a more discriminating correlate of clinical VAD (conjunctival xerophthalmia) than other anthropometric indicators in both bivariate and multivariate analyses. Where VAD is endemic, the use of the standardized MUAC may allow for targeting of resources to children with marginal muscle mass. This may ensure the greatest reduction in VAD, along with it's associated morbidity and mortality. Additional studies are proposed to confirm the usefulness and validity of the MUAC z-scores as an independent, and absolute indicator of protein status, and to serve as a screening tool to identify children at risk for protein deficiency.