Understanding Mid-Upper Arm Circumference (MUAC)
Mid-Upper Arm Circumference (MUAC) is a vital anthropometric measurement used to assess nutritional status, particularly in young children and pregnant women. The measurement is taken at the midpoint of the upper arm and reflects the body's muscle and fat mass, which are depleted during periods of malnutrition. Its simplicity and accuracy make it an essential tool in community-based screening, especially in humanitarian and low-resource settings where weighing scales and other equipment may be unavailable.
How to Measure MUAC Correctly
Accurate measurement is crucial for correct diagnosis. Specialized, color-coded MUAC tapes are often used for children, but a standard non-stretchable measuring tape can also be used, especially for adults.
Here are the steps for proper measurement:
- Position the person: Have the person stand or sit with their left arm bent at a 90-degree angle at the elbow, parallel to their body. If the left arm cannot be used, the right arm is acceptable.
- Find the midpoint: Measure the distance between the bony part of the shoulder and the tip of the elbow. Mark the midpoint with a pen.
- Relax the arm: Ask the person to relax their arm and let it hang loosely at their side. Flexing the arm can alter the reading.
- Wrap the tape: Wrap the MUAC tape snugly around the arm at the marked midpoint. Ensure the tape is not too tight or too loose and lies flat against the skin.
- Record the reading: Read the measurement where the tape overlaps. For color-coded tapes, the nutritional status is indicated by the color zone. For standard tapes, record the value to the nearest millimeter.
WHO Guidelines: Arm Circumference for Children (6–59 months)
The World Health Organization (WHO) provides clear, globally recognized guidelines for classifying acute malnutrition in children aged 6 to 59 months using MUAC. These cut-offs are critical for identifying children at high risk of morbidity and mortality.
- Severe Acute Malnutrition (SAM): A MUAC of less than 115 mm (< 11.5 cm) indicates severe acute malnutrition. Children with SAM are at a significantly increased risk of death and require urgent therapeutic feeding. Bilateral pitting oedema is also an independent indicator of SAM.
- Moderate Acute Malnutrition (MAM): A MUAC measurement between 115 mm (11.5 cm) and less than 125 mm (< 12.5 cm) signifies moderate acute malnutrition. Children in this category need supplementary feeding and close monitoring to prevent their condition from worsening.
- No Acute Malnutrition: A MUAC of 125 mm (12.5 cm) or greater indicates no acute malnutrition.
Arm Circumference for Adults and Other Groups
MUAC is also a useful screening tool for older children, adolescents, adults, and specific groups like pregnant women, although the cut-off values differ. While Body Mass Index (BMI) is a common metric for adults, MUAC can be especially valuable in clinical settings where height and weight are difficult to measure.
- Adults: A MUAC value of less than 24 cm often indicates acute malnutrition in adult women, while a measurement of less than 25 cm is used for men. Some protocols may use a cutoff of <17cm for severe malnutrition in adults.
- Older children and adolescents (5-18 years): For these age groups, BMI-for-age z-scores are the standard, but MUAC can still offer a useful screening perspective.
- Pregnant and Lactating Women: For these women, a MUAC less than 16 cm may indicate severe acute malnutrition.
MUAC vs. Weight-for-Height Z-score (WHZ)
Both MUAC and Weight-for-Height Z-score (WHZ) are recommended by the WHO for diagnosing acute malnutrition, but they identify different populations and have distinct strengths. The choice of which indicator to prioritize often depends on the context and resources available.
| Feature | Mid-Upper Arm Circumference (MUAC) | Weight-for-Height Z-score (WHZ) |
|---|---|---|
| Measurement | Simple, uses a non-stretchable tape measure. | Requires a weighing scale and stadiometer/infantometer. |
| Resource Needs | Low-cost and minimal training required; ideal for community-based screening. | Requires more equipment and training; primarily used in health facilities. |
| Identification | Tends to identify younger children with SAM more effectively and is a stronger predictor of mortality risk. | Identifies a different, often older, population of malnourished children and is considered the gold standard in clinical settings. |
| Accuracy | High specificity but can have low sensitivity, potentially missing some cases. | Can miss certain types of malnutrition, and concordance with MUAC varies significantly. |
| Bias | Single cut-off value does not account for age or gender, leading to some age-related bias. | Z-score accounts for gender and age, providing a more detailed anthropometric assessment. |
Addressing Discrepancies and Contextual Adaptations
Studies have repeatedly shown poor concordance between MUAC and WHZ, meaning they identify different sets of malnourished children. This discrepancy is partly due to biological variations and different body compositions identified by each measure. For instance, MUAC is strongly related to fat mass, while WHZ reflects overall body mass relative to height.
As a result, some regions have investigated or adopted adjusted MUAC cut-offs to improve screening accuracy for their specific populations. For example, some studies in Vietnam suggested a higher optimal MUAC cut-off of 13.5 cm to improve the detection of severe acute malnutrition (SAM). In humanitarian efforts, the use of MUAC alone or in combination with WHZ and oedema is decided based on resource availability and local validation.
Community-based management of acute malnutrition (CMAM) often leverages MUAC for screening by community health workers, allowing for early detection and timely referral to treatment programs. UNICEF actively promotes the use of MUAC bands for detecting severe malnutrition and saving lives.
Conclusion
In summary, the specific arm circumference for acute malnutrition is defined by Mid-Upper Arm Circumference (MUAC) cut-off points, with standards varying for different age groups. The World Health Organization defines severe acute malnutrition in children aged 6–59 months as a MUAC below 115 mm and moderate acute malnutrition between 115 mm and 125 mm. This quick, low-cost screening method is a cornerstone of humanitarian and public health efforts for early detection. While its diagnostic accuracy can vary by population compared to other indicators like Weight-for-Height Z-score, its high specificity for mortality risk makes it an indispensable tool for identifying those most in need of urgent care. Its effectiveness is maximized when used as part of a comprehensive strategy that includes continued monitoring, treatment with therapeutic foods, and addressing the underlying causes of malnutrition. For more information on malnutrition management, consult reliable sources such as the World Health Organization (WHO) or UNICEF guidelines.
For more detailed protocols, the World Health Organization offers extensive documentation on malnutrition management.
