What is a MUAC Score?
MUAC, or Mid-Upper Arm Circumference, is a measurement of the circumference of a person's upper arm at its midpoint. It is a fast, simple, and effective screening tool for determining nutritional status, particularly for detecting malnutrition in children aged 6 to 59 months. The measurement reflects the amount of muscle and subcutaneous fat in the arm, which decreases during periods of undernutrition. Its simplicity makes it ideal for use in community-based settings and humanitarian emergencies where traditional equipment for measuring height and weight may be unavailable or impractical. The tool's accuracy in predicting mortality risk in children is a key reason for its widespread use by organizations like the World Health Organization (WHO), UNICEF, and Médecins Sans Frontières (MSF).
How to measure the MUAC score
Measuring MUAC correctly is a straightforward process that requires minimal training. It is typically performed on the left arm of the individual, following these steps:
- Locate the midpoint: The arm is bent at a 90-degree angle. The midpoint is found between the acromion (the bony part of the shoulder) and the olecranon process (the tip of the elbow).
- Mark the spot: A pen is used to mark this exact midpoint.
- Position the tape: The subject's arm is then allowed to hang loosely and the special, flexible MUAC measuring tape is wrapped around the arm at the marked midpoint.
- Read the measurement: The tape is pulled snugly, but not so tight that it pinches the skin. The measurement is recorded to the nearest millimeter. Many MUAC tapes are color-coded to simplify interpretation in the field.
Interpreting the MUAC Score
For children aged 6 to 59 months, color-coded MUAC tapes provide a quick visual assessment of nutritional status. While exact cut-offs can vary slightly by organization and population, the standard WHO guidelines use the following classifications:
- Green zone (> 13.5 cm): Indicates the child is well-nourished.
- Yellow zone (12.5 cm to 13.5 cm): Suggests moderate acute malnutrition (MAM). Intervention with supplementary food and monitoring may be necessary.
- Red zone (< 12.5 cm): Signals severe acute malnutrition (SAM), which requires urgent therapeutic feeding and medical care due to the high risk of mortality.
For adults, MUAC can also be used as a screening tool, though the cut-offs are different. Studies suggest approximate cut-offs corresponding to specific BMI categories. For instance, a MUAC of <25.5 cm might indicate underweight, while a MUAC of ≥29.5 cm might suggest obesity. However, specific cut-offs can vary based on population, ethnicity, and other factors, and there is less international standardization for adults than for children.
MUAC's role in humanitarian aid and clinical settings
The MUAC score's greatest strength lies in its practicality for use in resource-limited and crisis situations, such as refugee camps or areas affected by famine. In these scenarios, the ability to rapidly screen large numbers of people with minimal equipment is essential. Community health workers can be quickly trained to use MUAC tapes, allowing for widespread screening and early case identification. This helps healthcare providers prioritize care for the most vulnerable, like young children with SAM, who are at the highest risk of death.
In developed settings, MUAC can complement other nutritional assessment tools. For example, it can be useful for assessing nutritional status in bedridden patients or those with conditions that make accurate weight and height measurements difficult, such as fluid retention or limb contractures.
Comparison: MUAC vs. Body Mass Index (BMI)
| Feature | MUAC (Mid-Upper Arm Circumference) | BMI (Body Mass Index) |
|---|---|---|
| Measurement | Simple tape measure around the upper arm. | Requires weight (scale) and height (stadiometer). |
| Equipment Needs | Very low cost, simple, and highly portable. | Requires more expensive, cumbersome equipment. |
| Field Use | Ideal for rapid community screening, especially in emergencies. | Challenging to use in remote areas or large-scale humanitarian crises due to equipment and logistics. |
| Population Focus | Particularly effective and reliable for children aged 6-59 months. | Widely used for adults, with varying relevance for children based on age-specific growth curves. |
| Predictive Value | Excellent predictor of mortality risk in children. | Good indicator of nutritional status and health risks in adults, but can be less reliable in certain populations (e.g., athletes). |
| Limitations | Standardized cut-offs are lacking for older children and adults across all populations. | Does not differentiate between fat and muscle mass. Difficult to use with immobile patients or those with fluid retention. |
Conclusion
The MUAC score is an invaluable and practical tool for quickly and accurately screening for malnutrition, especially among vulnerable populations and in emergency situations. Its simplicity, affordability, and high predictive value for mortality risk in young children make it an essential component of public health and humanitarian aid strategies. While it has limitations, particularly regarding the need for population-specific cut-offs for older children and adults, it remains a frontline tool for identifying those most in need of nutritional support. The continued use and standardization of the MUAC score are critical for preventing mortality and morbidity associated with acute malnutrition globally.
