What Is MUAC and How Is It Measured?
Mid-upper arm circumference (MUAC) is an easy and cost-effective anthropometric measurement used to assess nutritional status. Unlike the Body Mass Index (BMI), which requires both height and weight measurements, MUAC can be taken with a simple, non-stretchable tape measure and minimal training. This makes it particularly valuable in remote areas, for large-scale population surveys, or for individuals unable to stand, such as bedridden patients.
To measure MUAC in adults, follow these steps:
- Position the arm: Have the individual bend their non-dominant arm at a 90-degree angle, with the upper arm parallel to their body.
- Find the midpoint: Measure the distance between the bony part of the shoulder (acromion process) and the tip of the elbow (olecranon process). Mark the exact midpoint.
- Wrap the tape: Ask the person to let their arm hang loosely at their side. Wrap the MUAC tape snugly, but not too tightly, around the arm at the marked midpoint.
- Record the measurement: Read the result in centimeters to the nearest millimeter.
Why Are MUAC Cut-Offs Not Universal?
Despite its convenience, the absence of a single, universal MUAC cut-off for adults is a key consideration. Research indicates that optimal MUAC cut-offs vary significantly depending on several factors, primarily sex, age, and ethnicity. This variation is largely due to differences in body composition and fat distribution among diverse populations. For instance, a cut-off point validated in a young, medical student population in India might not be appropriate for older adults in Bangladesh.
Many studies correlate MUAC with BMI categories based on World Health Organization (WHO) standards to establish population-specific cut-offs. The derived values aim for high sensitivity (correctly identifying those with the condition) and specificity (correctly excluding those without it).
Examples of Population-Specific MUAC Cut-Offs
Several studies worldwide have proposed specific MUAC cut-offs for adult overweight and obesity based on local populations, highlighting the regional differences:
- Bangladesh (2025 Study): Using a large, nationally representative dataset, researchers established specific cut-offs based on sex and age against the WHO BMI classifications. For younger and middle-aged adults, the optimal cut-offs to detect overweight were $\geq28.5$ cm for males and $\geq26.5$ cm for females. The cut-off to detect obesity was $\geq29.5$ cm for males and $\geq28.5$ cm for females in these age groups.
- Sudan (2022 Study): A study on Sudanese adults found that a MUAC $\geq29.5$ cm could effectively screen for obesity (BMI $\geq30.0$ kg/m²) in both males and females, though optimal cut-offs for overweight were not specifically detailed.
- Ethiopia (2022 Study): Research among adult employees in Ethiopia suggested a single cut-off of 26.91 cm for both males and females to screen for combined overweight/obesity (BMI $\geq25$ kg/m²). However, this reflects a single population and may not apply broadly.
- South India (2022 Study): A study on medical students in South India proposed specific cut-offs to screen for overweight (BMI $\geq25$ kg/m²): 31.3 cm for men and 28.5 cm for women.
Comparison Table: MUAC vs. BMI
| Feature | Mid-Upper Arm Circumference (MUAC) | Body Mass Index (BMI) |
|---|---|---|
| Equipment Required | Simple, non-stretchable tape measure | Weight scale and stadiometer (for height) |
| Calculation | Direct measurement, no calculation needed | Formula: $weight (kg) / height^2 (m)$ |
| Resource Needs | Minimal and inexpensive, ideal for resource-limited areas | More costly and complex equipment, less portable |
| Feasibility | Excellent for bedridden patients, pregnant women (less variable) | Difficult or impossible for patients unable to stand |
| Training | Requires minimal training for accurate results | Requires trained personnel to minimize error in height measurement |
| Universal Cut-offs | No, cut-offs vary significantly by sex, age, and ethnicity | Provides a standard, but its application can vary (e.g., Asian populations) |
| Associated Risks | Can indicate risk of metabolic syndromes | Strong predictor of cardiovascular-related mortality |
Limitations of MUAC and Best Practices
While MUAC is an invaluable screening tool, it has limitations, especially when compared to gold-standard body fat measurement techniques like Dual Energy X-ray Absorptiometry (DEXA). MUAC doesn't differentiate between fat mass and fat-free (lean) mass, meaning a muscular person might have a high MUAC without being overweight.
Furthermore, while some studies propose single cut-off values for simplicity, these can reduce accuracy and don't fully account for variations across different groups. For this reason, using age- and sex-specific cut-offs, like those determined in the Bangladesh study, is considered a more accurate approach.
Conclusion
In conclusion, MUAC offers a simple, inexpensive, and practical method for screening overweight and obesity among adults, especially in community and resource-limited settings where standard BMI measurement is not feasible. There is no single universal MUAC cut-off for adults; rather, optimal thresholds vary significantly by sex, age, and ethnicity. Research from different countries has established specific cut-offs, underscoring the need for context-specific application. While not a replacement for more sophisticated body composition analysis, MUAC provides a highly useful proxy measure that can help identify individuals at higher risk of metabolic health issues. Integrating context-specific MUAC cut-offs into screening protocols is a valuable strategy for public health efforts to combat rising rates of overweight and obesity.
For more information on nutritional assessment methods, consult the BAPEN website(https://www.bapen.org.uk/must-and-self-screening/must-calculator/).
