What is Mid-Upper Arm Circumference (MUAC)?
Mid-Upper Arm Circumference (MUAC) is a measurement of the circumference of the upper arm, taken midway between the shoulder and the elbow. It serves as a simple, non-invasive, and portable tool for assessing nutritional status, particularly for identifying acute malnutrition or wasting. Unlike body mass index (BMI), MUAC is less influenced by factors like hydration and can be measured with minimal training and inexpensive equipment. This makes it an ideal tool for mass screenings in community-based healthcare settings and emergencies.
The Measurement Process
Measuring MUAC accurately is crucial for reliable results. The standard procedure involves finding the midpoint of the upper arm between the shoulder and elbow, then wrapping a non-stretchable tape around this point to read the circumference. For children, color-coded tapes are often used for easy risk identification.
Arm Circumference Cut-offs for Malnutrition by Group
The cut-off points for determining malnutrition based on MUAC differ significantly by age and condition, as guided by the World Health Organization (WHO).
Children (6–59 months)
MUAC is highly effective for identifying severe acute malnutrition (SAM) and moderate acute malnutrition (MAM) in young children. WHO cut-offs are: MUAC less than 115 mm for SAM, and between 115 mm and less than 125 mm for MAM. Normal nutritional status is indicated by a MUAC of 125 mm or greater.
Children and Adolescents (5–17 years)
Nutritional assessment for older children and adolescents also uses specific cut-offs. General guidelines suggest: for ages 5–9 years, < 135 mm for SAM and ≥135 to < 145 mm for MAM; for ages 10–14 years, < 160 mm for SAM and ≥160 to < 185 mm for MAM.
Adults
MUAC can be used in adults to screen for malnutrition and estimate BMI, especially when other measurements are difficult. General adult cut-offs are: < 185 mm for severe malnutrition, ≥ 185 mm to < 220 mm for moderate malnutrition, and ≥ 220 mm for normal status.
Pregnant and Postpartum Women
A MUAC cut-off of 23 cm or less is often used to identify pregnant women at risk of low birth weight infants. Screening during antenatal care helps provide targeted nutrition support.
Interpreting Colour-Coded MUAC Tapes
Color-coded tapes are used for rapid interpretation in community settings. Green indicates adequate nutrition, yellow signifies moderate malnutrition or risk, and red indicates severe acute malnutrition requiring immediate attention.
MUAC vs. Other Nutritional Assessments
MUAC is a valuable screening tool, but other methods like Weight-for-Height Z-score (WHZ) also exist. The table below compares these two common approaches.
| Feature | Mid-Upper Arm Circumference (MUAC) | Weight-for-Height Z-score (WHZ) |
|---|---|---|
| Measurement | Single, quick, and simple measurement of arm circumference | Requires two measurements (weight and height/length) and calculation |
| Equipment | Non-stretchable tape measure (often colour-coded) | Weighing scale, length/height board, and computer/chart for Z-score calculation |
| Prognostic Value | Strong predictor of mortality risk, particularly in community settings | Weaker predictor of all-cause mortality compared to MUAC in community settings |
| Identifies | Wasting of muscle and fat mass, making it sensitive to acute changes | Wasting based on weight relative to height, can be influenced by body shape |
| Training Required | Minimal training needed for accurate community-level use | Requires more training for precise measurements to avoid error |
| Case Overlap | MUAC and WHZ identify largely different, yet overlapping, groups of malnourished children | Complementary to MUAC but may miss some high-risk children identified by MUAC |
Limitations and Considerations of MUAC
MUAC has limitations. It doesn't identify the exact same individuals as WHZ, may show age and sex bias, and inconsistent tape design can affect accuracy. A low MUAC should prompt a more comprehensive nutritional assessment.
Conclusion
MUAC is a simple and effective screening tool for malnutrition across various groups, utilizing WHO cut-off points and color-coded tapes for quick identification of risk. While valuable for initial assessment and predicting mortality, it is best used as part of a comprehensive nutritional evaluation to ensure appropriate intervention. Understanding MUAC cut-offs is crucial for health professionals.
