Analysing concordance between MUAC, MUACZ, and WHZ in diagnosing acute malnutrition among children under five in Somalia

Background Acute malnutrition, also known as wasting, affected an estimated 45 million children under five (CU5) globally in 2023. Wasting is measured using a child’s mid upper arm circumference (MUAC), weight-for-height z-score (WHZ), or nutritional oedema. In low-resource contexts, MUAC is often the only measurement used to regularly screen for malnutrition, but recent research suggests MUAC alone fails to diagnose 25–80% of WHZ-wasted children. Mid upper arm circumference, an age-adjusted MUAC z-score, may identify additional cases missed by MUAC alone. Methods This was a secondary analysis of 1408 CU5 enrolled in a cluster-randomised controlled trial in two high-wasting regions of Somalia. This analysis explored wasting prevalences, concordance between indicator pairs, linear regression modelling, and receiver operating characteristic (ROC) analysis using WHZ as a reference standard to examine alternative MUAC and MUACZ thresholds. Results Wasting prevalence was 1.5% by MUAC, 8.5% by MUACZ, and 14.8% by WHZ. Mid upper arm circumference alone failed to identify 94% of WHZ-wasted children. There was slight concordance between MUAC and WHZ (kappa (κ) = 0.089) and fair concordance between MUACZ and WHZ (κ = 0.385). Linear regression indicated that MUAC, age, sex, and stunting were all statistically significant variables for estimating child WHZ. Using WHZ as a reference standard, a MUAC of 13.7cm and MUACZ of –0.9 both accurately diagnosed >82% of wasted children ages 9–23 months. A MUAC of 14.4 cm and MUACZ of −1 both accurately diagnosed >76% of wasted children ages 24–59 months. Conclusions Poor concordance between MUAC and WHZ should prompt review of wasting measurement guidelines for this population. Stratified analyses and regression modelling showed increased MUAC with age among CU5. MUACZ or age-specific MUAC thresholds may identify more truly wasted children, improving coverage of treatment interventions. Policymakers should examine how adapting screening guidelines impacts health facilities and treatment availability. Future studies should consider long-term outcomes and mortality associated with increased thresholds of MUAC and MUACZ. Registration The cluster-RCT is registered at ClinicalTrials.gov, ID: NCT06642012.