Understanding Mid-Upper Arm Circumference (MUAC)
Mid-Upper Arm Circumference (MUAC) is a straightforward and effective anthropometric measurement used to screen for malnutrition in adults, adolescents, and children. It measures the circumference of the upper arm, which reflects changes in both muscle mass and subcutaneous fat stores. When an individual experiences rapid weight loss due to poor nutrition, their arm circumference decreases, making MUAC a sensitive indicator of acute nutritional status. MUAC is especially useful in humanitarian crises, resource-limited areas, or for bedridden patients where more complex measurements like Body Mass Index (BMI) are challenging.
How to measure MUAC in adults
Measuring MUAC is a simple procedure that requires minimal training and equipment, typically a flexible, non-stretchable tape measure. The measurement is usually taken on the right arm, following these steps:
- Locate the midpoint: The person's arm should be bent at a 90-degree angle. The measurer finds the tip of the shoulder (acromion) and the tip of the elbow (olecranon). The midpoint between these two bones is marked with a pen.
- Relax the arm: The person then relaxes their arm, allowing it to hang freely at their side.
- Take the measurement: The tape measure is wrapped around the arm at the marked midpoint. It should be snug against the skin but not so tight as to cause an indentation.
- Record the result: The measurement is read in centimeters to the nearest millimeter. Some tapes are color-coded (red, yellow, green) for quick interpretation, though numerical values are the standard for adults.
What are the MUAC cutoffs for adult malnutrition?
The cutoffs for what is the MUAC for adult malnutrition vary depending on the population, age, gender, and specific context, such as a famine or clinical setting. However, several commonly used or studied benchmarks exist, often correlated with BMI classifications. A key takeaway is that no single, globally recognized cutoff exists for all adults.
- General Adult Cutoffs: For detecting underweight (correlating to BMI < 18.5 kg/m$^2$), a simple rule of thumb suggested by some studies is a MUAC
< 25 cmfor males and< 24 cmfor females. More recent research indicates slightly higher optimal cutoffs, such as $\le 26.5$ cm for underweight males and $\le 25.5$ cm for females. - Severity-based Cutoffs (WHO-aligned): The FANTA project, referencing data from African countries, highlights a range of values for classifying severity.
- Moderate acute malnutrition (MAM): MUAC typically falls in a range such as 18.5 to < 22.0 cm.
- Severe acute malnutrition (SAM): MUAC is typically below a lower threshold, such as < 18.5 cm.
- Emergency Settings (Famine): In extreme conditions like famine, even lower thresholds are used to identify the most severe cases at high risk of death. For instance, a MUAC
< 17 cmfor men and< 16 cmfor women might indicate extreme wasting.
MUAC vs. BMI: A comparison for malnutrition assessment
| Feature | Mid-Upper Arm Circumference (MUAC) | Body Mass Index (BMI) |
|---|---|---|
| Procedure | Measures arm circumference with a tape. Quick, simple, and non-invasive. Can be done on bedridden patients. | Requires measuring height and weight, then a calculation ($kg/m^2$). Requires the patient to stand. |
| Equipment | Simple tape measure. Often color-coded for quick screening. | Weighing scale and height board. More expensive and less portable. |
| Accuracy | Good correlation with BMI, especially for detecting underweight. Reflects changes in fat and muscle stores. | Longstanding, widely accepted standard for nutritional status assessment. |
| Limitations | No universally standardized cutoffs for adults across all populations. May be less sensitive to long-term changes than BMI. | Can be challenging for bedridden, immobilized, or elderly patients. Less useful in famine conditions where quick screening is needed. |
| Best Used | For rapid screening in resource-limited or emergency settings, and for bedridden patients. | In clinical or research settings for a comprehensive assessment of nutritional status. |
The importance of nutrition diet following MUAC screening
Identifying malnutrition using MUAC is just the first step; the core of the intervention is the subsequent nutrition diet. A low MUAC reading signals the need for a comprehensive nutritional assessment and a tailored dietary plan. Depending on the severity, this could range from simple dietary counseling to specialized therapeutic feeding programs.
For moderate malnutrition, dietary guidance focuses on improving the intake of energy-dense, protein-rich foods to help rebuild muscle and fat stores. This might involve recommending locally available nutritious foods or providing fortified food supplements. For severe malnutrition, immediate and intensive interventions are necessary to prevent death. This involves therapeutic feeding with specific formulas designed for rapid and safe nutritional rehabilitation.
Dietary interventions must be customized to the individual's needs, considering any underlying health conditions, such as HIV or TB, which can exacerbate malnutrition. A nutrition professional uses the MUAC screening result to initiate and monitor the effectiveness of the dietary intervention over time, with regular follow-up measurements providing a crucial indicator of recovery.
For more information on community-based malnutrition management, visit the UNICEF supply website.
Conclusion
MUAC is an invaluable screening tool for adult malnutrition, offering a quick, simple, and cost-effective method to identify individuals in urgent need of nutritional support. While not a replacement for a full nutritional assessment, its strong correlation with BMI and ease of use make it particularly effective in settings with limited resources or where patients cannot be weighed or measured for height. The interpretation of MUAC cutoffs is context-dependent, but once malnutrition is identified, it serves as a critical trigger for implementing a targeted nutrition diet intervention to restore health and prevent further deterioration.
