Understanding the Mid-Upper Arm Circumference (MUAC)
The Mid-Upper Arm Circumference (MUAC) is a simple, effective, and non-invasive tool used to assess a person's nutritional status, especially in children aged 6 to 59 months. It is a measure of the muscle and subcutaneous fat in the upper arm, which are often depleted during acute malnutrition or wasting. In resource-limited settings, MUAC is favored over other methods like weight-for-height z-scores (WHZ) because it requires minimal training and inexpensive equipment, making it ideal for community-level screening. By identifying individuals with low MUAC values, healthcare providers and aid workers can quickly identify those at the highest risk of mortality and refer them for life-saving treatment.
Standard WHO MUAC Cut Offs for Children (6–59 months)
The World Health Organization (WHO) provides standardized MUAC cut off points for children aged 6 to 59 months. These cutoffs are often represented by color-coded tapes (red, yellow, and green) for easy interpretation by community health workers.
- Severe Acute Malnutrition (SAM): A MUAC reading of less than 115 mm (< 11.5 cm) indicates severe acute malnutrition, signaling a high risk of mortality that requires urgent medical intervention. This is typically indicated by the red zone on a MUAC tape.
- Moderate Acute Malnutrition (MAM): A MUAC reading of 115 mm to less than 125 mm (11.5 cm to < 12.5 cm) indicates moderate acute malnutrition. These children require supplementary feeding and regular monitoring to prevent their condition from deteriorating. This corresponds to the yellow zone.
- Normal Nutritional Status: A MUAC reading of 125 mm or greater (≥ 12.5 cm) is considered normal and is indicated by the green zone.
MUAC Cutoffs for Older Children, Adolescents, and Adults
While the 6–59 month guidelines are widely used, MUAC cutoffs for older populations can vary based on specific local guidelines and research findings. The Food and Nutrition Technical Assistance III Project (FANTA) has provided some references for classification.
- Children (5–9 years): Some guidelines classify SAM as a MUAC < 135 mm and MAM as ≥ 135 mm to < 145 mm.
- Children (10–14 years): For this age group, SAM may be defined as a MUAC < 160 mm and MAM as ≥ 160 mm to < 185 mm.
- Adolescents (15–17 years) and Adults: MUAC < 185 mm is a potential cutoff for SAM, and ≥ 185 mm to < 220 mm for MAM. Some research has suggested a MUAC of 24.5 cm to identify underweight in adults, corresponding to a BMI < 18.5 kg/m².
- Pregnant and Postpartum Women: Specific cutoffs are also used for this vulnerable group. Some guidelines define SAM as MUAC < 190 mm and MAM as ≥ 190 mm to < 230 mm. Humanitarian agencies have also used cutoffs such as < 210 mm for severe wasting.
How to Measure MUAC Correctly
Accurate measurement is critical for correct diagnosis. Here are the steps for a proper MUAC measurement:
- Locate the midpoint: Bend the person's left arm at a 90-degree angle. Use a non-stretch tape measure to find the midpoint between the tip of the shoulder (acromion) and the tip of the elbow (olecranon). Mark this midpoint.
- Straighten the arm: Ask the person to straighten and relax their arm.
- Wrap the tape: Wrap the MUAC tape snugly around the arm at the midpoint, ensuring it lies flat against the skin without being too tight or too loose.
- Read the measurement: Read the measurement in centimeters and millimeters where the arrows on the tape meet.
- Record and interpret: Record the measurement and interpret the nutritional status based on the appropriate cut off point for the person's demographic.
MUAC vs. Weight-for-Height Z-score (WHZ)
MUAC and WHZ are both methods for assessing acute malnutrition, but they have distinct applications and characteristics. A comparison helps illustrate their respective roles in nutritional screening and assessment.
| Feature | MUAC | Weight-for-Height Z-score (WHZ) |
|---|---|---|
| Application | Primary tool for community-level screening, often during emergencies or in settings with limited resources. | Considered the gold standard for clinical diagnosis of malnutrition. |
| Ease of Use | Simple, quick, and requires minimal training, making it ideal for community health workers or even family members. | Requires more equipment (scales, measuring boards) and trained personnel, making it less practical for mass screening. |
| Equipment | Simple, non-stretch, color-coded tape. | Weighing scale and height board. |
| Mortality Predictor | A strong and independent predictor of mortality risk in children. | Also a strong predictor of mortality, but often identifies a different subset of malnourished children than MUAC. |
| Correlation with WHZ | MUAC and WHZ can identify different groups of children, meaning they don't perfectly overlap. Recent research suggests different optimal cutoffs to improve congruence. | Identifies malnourished children based on body mass relative to height. |
The Path Forward: Addressing Malnutrition After Screening
Early detection of malnutrition using MUAC is just the first step. Once a person is identified as malnourished, they must be linked with appropriate care. This typically involves referral to a therapeutic feeding program, such as the Community-based Management of Acute Malnutrition (CMAM). Treatment plans include specially formulated foods like Ready-to-Use Therapeutic Food (RUTF) for severe cases or Supplementary Foods for moderate cases. Medical staff also manage complications like infections, dehydration, and micronutrient deficiencies. Comprehensive care, including follow-up and nutritional education, is vital for a full recovery and to prevent relapse.
Conclusion
The MUAC cut off points provide a simple yet powerful means of screening for malnutrition, particularly for those most vulnerable, like young children. The standardized WHO cutoffs for children aged 6 to 59 months are a cornerstone of many public health programs. For older children, adults, and pregnant women, various guidelines and research-based cutoffs exist, though universal consensus is still evolving. Accurate measurement and proper interpretation are essential for timely intervention and improved health outcomes. MUAC's ease of use makes it a crucial tool for saving lives by identifying at-risk individuals early and facilitating their access to proper nutritional support and medical care. The effectiveness of any screening program ultimately depends on the promptness and quality of the follow-up treatment provided.
