Understanding the Mid-Upper Arm Circumference (MUAC)
Mid-Upper Arm Circumference, or MUAC, is a simple, effective anthropometric measurement used to assess a person's nutritional status, primarily for screening purposes in field settings. It is the circumference of the upper arm, measured at the midpoint between the tip of the shoulder (acromion process) and the tip of the elbow (olecranon process). This measurement is particularly valuable in low-resource areas because it is inexpensive, requires minimal training, and does not depend on access to scales or measuring boards. It is especially critical for identifying acute malnutrition in vulnerable populations, such as children aged 6 to 59 months and pregnant women.
The measurement reflects changes in muscle mass and subcutaneous fat stores, providing a reliable proxy for overall body composition. Unlike Body Mass Index (BMI), which can be unreliable for individuals who cannot stand or have fluid retention, MUAC provides a more consistent indicator of nutritional status in these cases. While a single MUAC measurement can indicate current nutritional status, repeated measurements can help monitor a person's response to nutritional support.
Normal MUAC Ranges by Population Group
Normal MUAC values differ significantly based on age, gender, and physiological status, such as pregnancy. The World Health Organization (WHO) and other humanitarian organizations provide standardized cut-offs to classify nutritional status.
Infants (under 6 months)
For very young infants, specialized 'Mother-Infant MUAC' tapes are used to screen children from 6 weeks to 6 months.
- Normal: Ranges vary, but a MUAC of 11 cm and above is generally considered normal for infants 6 weeks to 6 months.
- Risk: Values below 11 cm may indicate underweight or severe underweight.
Children (6–59 months)
This is the most common age group for MUAC screening, often using a color-coded tape to simplify assessment.
- Normal (Green): $\ge 12.5$ cm.
- Moderate Acute Malnutrition (MAM) (Yellow): $\ge 11.5$ cm to $<12.5$ cm.
- Severe Acute Malnutrition (SAM) (Red): $< 11.5$ cm.
Adolescents (10–19 years)
For adolescents, the MUAC cut-offs are higher and can be gender-specific to align with Body Mass Index-for-age z-scores (BAZ).
- Normal (Age 10-14): $\ge 18.5$ cm.
- Moderate Acute Malnutrition (MAM) (Age 10-14): $\ge 16$ cm to $< 18.5$ cm.
- Severe Acute Malnutrition (SAM) (Age 10-14): $< 16$ cm.
- Normal (Age 15-17): $\ge 22$ cm (boys), $\ge 20$ cm (girls).
Adults
Standardized cut-offs for non-pregnant adults are used to screen for underweight, but can also screen for overweight and obesity.
- Normal (non-pregnant adults): $\ge 22$ cm (females) and $\ge 23$ cm (males) is often cited in studies, although a universal cut-off is debated. The global standard for underweight is often considered MUAC $<24$ cm.
- Underweight (Risk): $<24$ cm for both sexes, aligning with BMI $<18.5$ kg/m2.
- Overweight/Obesity (Risk): MUAC values indicating overweight or obesity vary by population, but may be over 27 cm.
Pregnant and Postpartum Women
MUAC is a reliable tool for assessing nutritional risk in pregnant women, as it changes very little during pregnancy.
- Normal (Low Risk): $>23$ cm.
- Risk of Malnutrition: $<23$ cm, which can be linked to a risk of low birth weight.
- Severe Malnutrition (Emergency Settings): Often $<21$ cm is used for admission to feeding programs, though a higher cut-off of 23 cm is recommended for more inclusive screening.
Comparison of MUAC Ranges by Demographic
| Demographic | Normal MUAC Range (cm) | Malnutrition (Risk/MAM) (cm) | Severe Acute Malnutrition (SAM) (cm) |
|---|---|---|---|
| Infants (6wks–6mo) | $\ge 11.0$ | N/A | Varies, can be $< 10.9$ |
| Children (6–59 mo) | $\ge 12.5$ | $11.5$ to $< 12.5$ | $< 11.5$ |
| Adolescents (10–14 yr) | $\ge 18.5$ | $16$ to $< 18.5$ | $< 16$ |
| Adults (non-pregnant) | $>24$ | $<24$ (underweight) | Variable |
| Pregnant Women | $>23$ | $<23$ | $<21$ (emergency) |
How to Accurately Measure MUAC
Accurate measurement is crucial for reliable results. Health workers are typically trained to follow these steps:
- Have the person's left arm hanging relaxed by their side.
- Locate the tip of the shoulder (acromion) and the tip of the elbow (olecranon).
- Measure the distance between these two points using a non-stretchable MUAC tape.
- Find the midpoint and mark it with a pen.
- Wrap the tape around the arm at this midpoint, ensuring it is flat against the skin and not too tight or too loose.
- Read the measurement to the nearest 0.1 cm.
For more information on the types of MUAC tapes and their specific uses, see the UNICEF supply catalogue.
The Importance of MUAC as a Screening Tool
MUAC's primary advantage is its simplicity and speed, which makes it an excellent community-level screening tool. Early identification of malnutrition is critical, especially in children, as it allows for prompt intervention to prevent further deterioration of health and mortality. MUAC is particularly useful in emergency situations and for community-based programs where resources are limited and large-scale, rapid screening is necessary. However, it is essential to remember that MUAC is a screening tool, and those identified with malnutrition should receive a more comprehensive clinical assessment and appropriate medical nutrition therapy. The interpretation of results should always consider the specific population's context, as cut-offs can vary based on regional differences in body composition.
Conclusion
Understanding what is the normal MUAC range is foundational for effective nutritional screening, particularly in vulnerable populations and resource-limited settings. By using standardized, and sometimes color-coded, MUAC tapes, health professionals and trained community workers can rapidly identify individuals at risk of malnutrition and facilitate access to life-saving nutritional support. While normal ranges vary by age, gender, and physiological state, MUAC remains a reliable, practical indicator for initial assessment. Correct measurement technique and awareness of specific cut-offs are key to ensuring the accuracy and efficacy of this vital public health tool.
