Understanding Mid-Upper Arm Circumference (MUAC)
Mid-Upper Arm Circumference (MUAC) is an anthropometric measurement used to assess nutritional status, particularly for screening malnutrition in individuals where weighing and measuring height might be impractical, such as in resource-limited or emergency settings. MUAC measures the circumference of the upper arm at its midpoint, providing an indicator of both muscle mass and subcutaneous fat stores. Due to its simplicity, low cost, and speed, MUAC has become a vital tool in global health initiatives, especially for identifying acute malnutrition in young children and pregnant women.
How to Accurately Measure MUAC
For the most reliable results, MUAC should be measured on the left, non-dominant arm, following a standardized procedure. The measurement should be taken by a trained individual, but the process can be easily learned. Here is a step-by-step guide:
- Ask the subject to bend their left arm at a 90-degree angle, with the elbow pointing downwards.
- Locate the bony protrusion of the shoulder (acromion) and the tip of the elbow (olecranon process).
- Measure the distance between these two points with a non-stretchable measuring tape.
- Identify and mark the midpoint of this distance on the outer side of the arm.
- Ask the subject to relax their arm, letting it hang loosely by their side.
- Wrap the measuring tape around the arm at the marked midpoint, ensuring it is snug but not tight. The tape should be flat against the skin.
- Read the measurement to the nearest millimeter and record the result.
- For children, many tapes use color-coded bands to make interpretation quick and easy.
Interpreting MUAC Measurements for Nutritional Status
Interpretation of MUAC measurements relies on established cut-off points, which vary by age and population group. For children aged 6 to 59 months, color-coded tapes are commonly used.
MUAC Cut-offs for Children (6-59 months)
- Green Band: ≥ 125 mm indicates normal nutritional status.
- Yellow Band: ≥ 115 mm to < 125 mm indicates moderate acute malnutrition (MAM).
- Red Band: < 115 mm indicates severe acute malnutrition (SAM) and requires urgent medical attention.
MUAC Cut-offs for Adults and Adolescents
For adults and adolescents, MUAC cut-offs are used to screen for underweight and obesity, often correlating with Body Mass Index (BMI) ranges.
- Normal: ≥ 220 mm.
- Moderate Malnutrition: ≥ 185 mm to < 220 mm.
- Severe Malnutrition: < 185 mm.
- Potential Underweight: < 235 mm (suggests BMI likely less than 20).
- Potential Obesity: > 320 mm (suggests BMI likely more than 30).
- Specific research on adult populations, such as in Bangladesh, has derived more specific age- and sex-based cut-offs for underweight, overweight, and obesity.
MUAC vs. BMI: A Nutritional Assessment Comparison
MUAC and BMI are both tools for nutritional assessment, but they differ significantly in their application and logistics. The following table highlights their key differences:
| Feature | Mid-Upper Arm Circumference (MUAC) | Body Mass Index (BMI) |
|---|---|---|
| Equipment | Simple, non-stretchable measuring tape or color-coded band. | Digital scale and stadiometer (height measurement device). |
| Resource Needs | Minimal and low-cost. | More resource-intensive due to equipment and space requirements. |
| Ease of Use | Very simple, requires minimal training. | More complex, requires accurate height and weight measurements. |
| Speed | Very fast and portable for rapid screening. | Slower, may be challenging in field or emergency settings. |
| Applicability | Highly effective in children (6-59 months), pregnant women, and ill/non-ambulatory adults. | Standard for general adult populations but impractical for certain groups. |
| Indicator of | Reflects fat and muscle mass, especially useful for acute energy deficiency. | General indicator of weight for height, does not distinguish between fat and muscle. |
Limitations and Important Considerations
While MUAC is an invaluable tool, it has limitations. Measurement errors can occur from incorrect tape placement, improper tension, or inaccurate reading. MUAC cut-offs can vary between different populations and specific conditions. For instance, children with cerebral palsy may have different optimal MUAC cut-offs. In cases of edema (swelling), MUAC measurements can be skewed. It is also less specific than BMI for assessing overweight and obesity in adults compared to its high accuracy for identifying undernutrition. Regular training and adherence to standardized protocols are essential for accurate and consistent results.
Conclusion
Mid-Upper Arm Circumference is a quick, simple, and effective tool for nutritional screening, particularly for detecting malnutrition in vulnerable populations like young children. Its low cost and ease of use make it ideal for community-based health programs and emergency relief efforts. While not a definitive diagnostic tool for all nutritional issues and having some limitations, it serves as a crucial first-line indicator. Consistent measurement and appropriate interpretation based on established cut-off points are key to leveraging its benefits for improving global health and nutrition outcomes.
For more information on MUAC tapes and their use in humanitarian contexts, visit UNICEF's Supply Division on Mid-upper arm circumference (MUAC) measuring tapes.
