Inconsistent diagnosis of acute malnutrition by weight-for-height and mid-upper arm circumference: contributors in 16 cross-sectional surveys from South Sudan, the Philippines, Chad, and Bangladesh

Abstract

BackgroundThe two anthropometric indicators of acute malnutrition in children under 5 years, i.e. a Mid-Upper Arm Circumference < 125 mm (MUAC125) or a Weight-for-Height Z-score<−2 (WHZ−2), correlate poorly. We aimed at assessing the contribution of age, sex, stunting (Height-for-Age HAZ<−2), and low sitting-standing height ratio Z-score (SSRZ in the 1st tertile of the study population, called hereafter ‘longer legs’) to this diagnosis discrepancy.MethodsData from 16 cross-sectional nutritional surveys carried out by Action Against Hunger International in South Sudan, the Philippines, Chad, and Bangladesh fed multilevel, multivariate regression models, with either WHZ−2 or MUAC125 as the dependent variable and age, sex, stunting, and ‘longer legs’ as the independent ones. We also compared how the performance of MUAC125 and WHZ−2 to detect slim children, i.e. children with a low Weight-for-Age (WAZ<−2) but no linear growth retardation (HAZ≥−2), was modified by the contributors.ResultsOverall 23.1 % of the 14,409 children were identified as acutely malnourished by either WHZ−2 or MUAC125, but only 28.5 % of those (949/3,328) were identified by both indicators. Being stunted (+17.8 %; 95 % CI: 14.8 %; 22.8 %), being a female (+16.5 %; 95 % CI: 13.5 %; 19.5 %) and being younger than 24 months (+33.6 %; 95 % CI: 30.4 %; 36.7 %) were factors strongly associated with being detected as malnourished by MUAC125 and not by WHZ−2, whereas having ‘longer legs’ moderately increased the diagnosis by WHZ−2 (+4.2 %; 95 % CI: 0.7 %; 7.6 %). The sensitivity to detect slim children by MUAC125 was 31.0 % (95 % CI: 26.8 %; 35.2 %) whereas it was 70.6 % (95 % CI: 65.4 %; 75.9 %) for WHZ−2. The sensitivity of MUAC125 was particularly affected by age (57.4 % vs. 18.1 % in children aged < 24 months vs. ≥ 24 months). Specificity was high for both indicators.ConclusionsMUAC125 should not be used as a stand-alone criterion of acute malnutrition given its strong association with age, sex and stunting, and its low sensitivity to detect slim children. Having ‘longer legs’ moderately increases the diagnosis of acute malnutrition by WHZ−2. Prospective studies are urgently needed to elucidate the clinical and physiological outcomes of the various anthropometric indicators of malnutrition.

Weight-for-height and mid-upper-arm circumference should be used independently to diagnose acute malnutrition: policy implications

“…The available data suggests that the limbs of these latter children are not proportionately long and at least for these populations variation in limb length is an inadequate explanation for the much greater proportion of children diagnosed by WHZ and not by MUAC. This conclusion is supported by an analysis by Roberfroid et al [26]. They examined the relationship between WHZ and MUAC from 16 surveys in which sitting height had been measured and concluded that leg length had a minor effect upon the discrepancy and that other factors were dominant.…”

Low mid-upper arm circumference identifies children with a high risk of death who should be the priority target for treatment

“…Briend et al misquote our paper and consistently misquote Roberfroid et al's paper [34,35,49] which both show that long-legs have a minor effect on WHZ which is inadequate to explain the discrepancies between WHZ and MUAC in diagnosing SAM. There are many societies shown in our paper where long-legs cannot be the cause for the dramatic discrepancy between MUAC-SAM and WHZ-SAM.…”

Examining Mid‐Upper Arm Circumference Malnutritionz‐Score Thresholds

“…There are a number of studies that demonstrate the lack of clear agreement between anthropometric indices for identifying malnutrition. Specifically, BMI, WL, and MUAC tend to identify different proportions of children with malnutrition . This may be explained, in part, because the majority of studies mix comparisons between age‐specific/gender‐specific criteria (WLz or BMIz) and absolute value based‐criteria (MUAC in centimeters), though it is well supported that z ‐score‐based classifications are accompanied by greater sensitivity and less bias than absolute value cutoffs .…”

“…Specifically, BMI, WL, and MUAC tend to identify different proportions of children with malnutrition. 18,19 This may be explained, in part, because the majority of studies mix comparisons between age-specific/gender-specific criteria (WLz or BMIz) and absolute value based-criteria (MUAC in centimeters), though it is well supported that z-score-based classifications are accompanied by greater sensitivity and less bias than absolute value cutoffs. 8,[20][21][22][23][24][25][26][27] In a 2014 consensus document, AND/ASPEN thoughtfully recommended indicators of pediatric malnutrition that were evidence based, inexpensive, easy to use, reproducible, and sensitive for both screening and longitudinal monitoring.…”