Concordance between the estimates of wasting measured by weight-for-height and by mid-upper arm circumference for classification of severity of nutrition crisis: analysis of population-representative surveys from humanitarian settings

BACKGROUND: Despite frequent use of mid-upper arm circumference (MUAC) to assess populations at risk of nutrition emergencies, as well as evidence that measurement of children based on MUAC identifies different children than weight-for-height (WHZ) as wasted, no crisis classification thresholds based on prevalence of wasting by MUAC currently exist. METHODS: We analyzed 733 population-representative anthropometric surveys from 41 countries conducted by Action Contre la Faim (ACF) and the United Nations High Commissioner for Refugees (UNHCR) between 2001 and 2016. Children aged 6–59 months were classified as wasted if they had a WHZ < − 2 and/or a MUAC < 125 mm. Prevalence of wasting as assessed by WHZ and by MUAC were compared using correlations and linear regression models adjusting for stunting prevalence, sex and age distribution of the sample. Median prevalence of wasting by MUAC corresponding to each of the WHZ-based crisis thresholds was examined. RESULTS: Median prevalence of wasting by WHZ was 10.47% (IQR: 6.34–17.55%) and by MUAC was 6.66% (IQR:4.12–10.88%). Prevalence of wasting by WHZ exceeded prevalence by MUAC in 543 (74.1%) surveys and median prevalence by WHZ was greater in 30 (73.17%) countries. Prevalence of wasting by WHZ is poorly correlated with prevalence of wasting by MUAC (ρ = 0.55). R(2) was 0.36 for unadjusted and 0.45 for adjusted linear regression model. The difference between the prevalence by WHZ and by MUAC increased as the overall prevalence by WHZ increased (ρ = 0.69). Surveys with prevalence of wasting by WHZ approximately equal to thresholds for “poor” (5% ± 2.5%), “serious” (10% ± 2.5%), “emergency” (15% ± 2.5%), and “famine” (30% ± 2.5%) were observed to have median prevalence of wasting by MUAC of 4.51% (IQR: 2.73–6.81%), 6.67% (IQR: 4.27–10.03%), 8.15% (IQR: 5.11–11.86%), and 15.71% (IQR: 10.28–17.50%), respectively. There was a very substantial overlap of MUAC values across the threshold categories. CONCLUSIONS: Given a poor correlation between population prevalence of wasting by WHZ and by MUAC, classification of surveys based on prevalence of wasting by MUAC will result in poor concordance with current WHZ-based crisis thresholds, even if regional differences are considered, regardless of the cutoffs used.