What is MUAC?
Mid-Upper Arm Circumference (MUAC) is a straightforward, non-invasive measurement used to assess nutritional status, particularly for screening malnutrition in children, but also increasingly in adults. The measurement is taken at the midpoint of the left upper arm, between the shoulder and the elbow. It is an effective indicator of a person's muscle and fat reserves and provides a quick and cost-effective way to identify individuals at risk. The use of color-coded tapes makes MUAC a highly accessible tool for community health workers and caregivers with minimal training.
Healthy MUAC Ranges by Age Group
The definition of a healthy MUAC varies significantly depending on age and, to a lesser extent, sex. Standardized cut-off points, often based on World Health Organization (WHO) guidelines, are used to classify nutritional status from normal to severely malnourished.
MUAC Ranges for Children
The most common use of MUAC is for children aged 6 to 59 months. For this group, a color-coded tape is typically used for rapid screening.
- Green: Not malnourished (≥ 12.5 cm).
- Yellow: Moderate acute malnutrition (MAM) (11.5 cm to < 12.5 cm).
- Red: Severe acute malnutrition (SAM) (< 11.5 cm).
For older children and adolescents, different cut-off points apply.
- Children 5–9 years: Healthy (≥ 14.5 cm), MAM (13.5 cm to < 14.5 cm), SAM (< 13.5 cm).
- Children 10–14 years: Healthy (≥ 18.5 cm), MAM (16.0 cm to < 18.5 cm), SAM (< 16.0 cm).
MUAC Ranges for Adults
While BMI is the standard for adult nutritional assessment, MUAC is a reliable alternative, especially in resource-limited settings or when height/weight measurement is impractical.
- Adults (non-pregnant): Healthy (> 21 cm), MAM (18 cm to < 21 cm), SAM (< 18 cm).
- Pregnant women: Healthy (≥ 23 cm), MAM (19 cm to < 23 cm), SAM (< 19 cm).
How to Measure MUAC Correctly
To ensure an accurate MUAC reading, proper technique is essential.
- Position the person with their left arm bent at a 90-degree angle.
- Locate the midpoint of the arm by measuring the distance between the tip of the shoulder bone (acromion) and the tip of the elbow (olecranon process).
- Mark this midpoint with a pen.
- Have the person relax their arm and let it hang naturally by their side.
- Wrap the MUAC tape snugly around the marked midpoint, ensuring it is flat against the skin and not too tight or too loose.
- Read the measurement from the tape where the arrows or markers meet.
MUAC vs. BMI: A Comparison
While Body Mass Index (BMI) is widely recognized, MUAC offers distinct advantages, particularly in certain contexts. Both tools are used for nutritional assessment, but their methods and applications differ.
| Feature | MUAC | BMI |
|---|---|---|
| Methodology | Single circumference measurement at the mid-upper arm. | Calculation based on weight and height (kg/m²). |
| Equipment | Non-stretchable, color-coded tape, inexpensive and portable. | Weighing scales and stadiometer, can be cumbersome. |
| Ease of Use | Simple and can be performed by minimally trained personnel. | Requires accurate height and weight measurements, which may be difficult for bedridden or very ill patients. |
| Indicator of | Body's immediate fat and muscle reserves. | General body size, correlated with total body fat. |
| Ideal Context | Community-level screening, emergency situations, pregnant women, resource-limited settings. | Clinical practice, research, and settings where accurate weight/height can be obtained. |
Limitations of MUAC Measurement
Despite its benefits, MUAC is not a perfect diagnostic tool and has several limitations that must be acknowledged.
- Variable Sensitivity: Studies have shown that the sensitivity of MUAC can be low, meaning it might miss some cases of malnutrition compared to the gold standard of Weight-for-Height Z-scores (WHZ). This issue varies significantly with age, with lower sensitivity in older children.
- Age and Sex Dependency: Optimal MUAC cut-off points can differ based on age, sex, and ethnicity, leading to inconsistent findings across studies. A single, universal cut-off may not be accurate for all populations.
- Operator Variability: Accuracy depends on correct measurement technique. If the tape is not placed at the correct midpoint or tensioned improperly, results can be unreliable. Training and standardization are crucial.
- Lack of Specificity: MUAC does not differentiate between fat and muscle mass and can be affected by factors like edema, which can give a falsely reassuring measurement.
The Role of MUAC in Public Health
MUAC's ease of use and low cost make it invaluable for community-based screening programs, particularly in low-resource settings. Community health workers and even caregivers can be trained to perform these measurements at the household level, enabling early detection of malnutrition before it becomes severe.
Regular community-level screening using MUAC can lead to earlier diagnosis, better program coverage, and a reduction in mortality and morbidity associated with malnutrition. This allows for timely referral to feeding programs or health facilities, reducing pressure on already strained healthcare systems. In addition, some programs have successfully integrated MUAC measurement with other assessments, such as evaluating maternal nutritional status, recognizing the link between maternal and child health.
For a deeper dive into the methodology and validation of MUAC against other metrics, a comprehensive study conducted in Sudan provides useful insights on its effectiveness in different populations, accessible at Mid-upper arm circumference as a substitute for body mass index among Sudanese adults.
Conclusion
What constitutes a healthy MUAC is not a single number but a context-dependent range based on age, sex, and health status. As a screening tool, MUAC is highly effective for rapid, community-based nutritional assessment due to its simplicity and low cost. While it serves as an excellent indicator for identifying those at risk, it is important to remember its limitations and consider it as part of a broader nutritional and health evaluation. Using MUAC, especially in vulnerable populations and emergency settings, is a critical step toward early detection and intervention for malnutrition.
