Validation of mid-upper arm circumference against to body mass index-for-age for assessing nutritional status among school adolescents in Ethiopia

Body mass index-for-age (BMI-for-age) is widely used indicator to assess the nutritional status of adolescent, however, its application in field settings can be challenging due to equipment and logistical constraints. Mid-upper arm circumference (MUAC) offers a simpler, low resource alternative, but its accuracy and validity among adolescents remain a subject of debate. This study aims to validate MUAC as a feasible alternative for assessing nutritional status in resource-limited settings like Ethiopia. Particularly, the study aimed to evaluate the screening performance of MUAC in detecting thinness compared to BMI-for-age Z-scores (BAZ) and to determine optimal MUAC cut-off points identifying undernutrition status among school students (10-19 years) in the West Hararge zone of Oromia, Ethiopia. A school based cross-sectional study was conducted involved 706 adolescents recruited from 10 schools in the West Harerghe Zone, Oromiia, Ethiopia. Participants were selected using a combination of simple random sampling at the school level and multistage sampling within schools. MUAC was measured on the left arm at the midpoint between the acromion and olecranon using a non-stretchable tape. Body mass index (BMI) was calculated from weight and height measurements taken using calibrated SECA electronic weighing scale (UNICEF) and a SECA portable stadiometer (SECA 213) respectively. All anthropometric measurements adhered to standardized World Health Organization (WHO) guidelines. The diagnostic performance of MUAC in predictor of thinness, as defined by BAZ was evaluated using sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver operating characteristic (ROC) curve analysis. The area under the ROC curve (AUC) for MUAC in detecting thinness compared to against BAZ was 0.76 (95% CI: 0.69-0.85) for adolescents aged 10-14 year group and 0.83 (95% CI: 0.68-0.96) for those aged 15-19 year group. Optimal MUAC cut-offs for detecting thinness were ≤ 19.85 cm the 10-14 year group and ≤ 22.1 cm for the 15-19 year group. For detecting severe thinness, the optimal cut-offs were ≤ 19.1 cm and ≤ 21.4 cm respectively, showed high sensitivity and specificity. MUAC demonstrated moderate effectiveness in detecting thinness among adolescents when compared to BAZ, with particularly high accuracy among those aged 10-14 years and 15-19 years. These findings support the use of MUAC is a reliable and feasible screening tool for undernutrition in resource limited settings. Age-specific MUAC cut-offs should be adopted for screening thinness in adolescents, particularly where BMI measurements are impractical. Further research and integration of MUAC into routine public health nutrition programs are recommended.