MUAC: Mid-Upper Arm Circumference
MUAC (Mid-Upper Arm Circumference) is an anthropometric measurement of the circumference of the upper arm taken at its midpoint, used to assess nutritional status, muscle mass, and body composition.
Definition and Measurement Technique
MUAC represents the circumference measured around the upper arm at the midpoint between the acromion process of the scapula and the olecranon process of the elbow 1.
Standardized Measurement Method
The measurement requires a flexible, non-stretchable tape measure (preferably metal) and follows this protocol 1:
- Patient positioning: Stand with elbow relaxed, right arm hanging freely at the side
- Landmark identification: Mark the midpoint between the acromion (shoulder) and olecranon (elbow) on the posterior arm surface
- Measurement: Place tape perpendicular to the arm shaft at the marked midpoint, pulling just snugly enough to ensure contact without compression
Clinical Applications
Nutritional Assessment Across Age Groups
MUAC serves as a practical screening tool for malnutrition, particularly valuable when standard measurements (weight, height) are difficult to obtain 2. Its utility varies significantly by age and clinical context:
Children (6-59 months)
- Acute malnutrition screening: MUAC <115 mm indicates severe acute malnutrition; 115-135 mm indicates moderate malnutrition 3
- Age-dependent performance: Shows moderate accuracy in children under 5 years (AUC 0.772) but excellent performance in ages 5-19 years (AUC 0.907) 4
- India-specific thresholds: MUAC <13.0 cm for severe wasting, <14.0 cm for wasting in children 6-59 months 5
Adolescents and Adults
MUAC demonstrates stronger diagnostic performance in older children and adults, with better correlation to BMI-based malnutrition indicators 4, 6. However, globally recognized cut-offs for adult malnutrition using MUAC remain unstandardized 7.
Body Composition Assessment
When combined with triceps skinfold thickness (TSF), MUAC allows calculation of mid-arm muscle area (MAMC) and arm muscle area (AMA), providing insight into lean body mass 1, 2:
- MAMC formula: MAC (cm) - π × TSF (cm)
- Corrected AMA for males: [(MAC - π × TSF)² / 4π] + 10 cm²
- Corrected AMA for females: [(MAC - π × TSF)² / 4π] + 6.5 cm²
Important caveat: AMA estimates may be inaccurate in obese and elderly subjects 1.
Clinical Context-Specific Considerations
When Standard Measurements Are Unreliable
MUAC becomes particularly valuable when fluid retention, edema, ascites, steroid treatment, or large tumor masses make weight measurements unreliable 2. In children with lower extremity edema or neurological disorders affecting skeletal structure, MUAC may provide a better indicator than weight-based indices 2.
Special Populations
Cerebral Palsy
In children with cerebral palsy, MUAC shows limited accuracy under 5 years (AUC 0.668) but good performance in ages 5-19 years (AUC 0.774), with higher malnutrition prevalence detected across all indices 4.
Pneumonia Risk Stratification
Children with pneumonia and MUAC 115-135 mm (moderate malnutrition) have 1.73 times higher odds of death (95% CI: 1.21-2.48), supporting its use for referral decisions in resource-limited settings 3.
Limitations and Pitfalls
Agreement with Other Indices
MUAC shows only fair-to-moderate agreement with WHZ (κ = 0.33) and moderate agreement with BMI-for-age (κ = 0.55) 6. It tends to identify a higher proportion of mild malnutrition compared to BMI-based classifications 6.
Age Dependency
The diagnostic utility of MUAC is strongly age-dependent, with markedly better performance in school-aged children and adolescents compared to early childhood 4. In children under 5 years, MUAC should complement rather than replace conventional anthropometric indices.
Population-Specific Thresholds
Different populations may require adjusted cut-offs. For example, optimal MUAC thresholds for predicting thinness and stunting in Sri Lankan schoolchildren were 167.5 mm and 162.5 mm respectively, differing after stratification by age and birth weight 8.
Practical Implementation
MUAC's primary advantage lies in its simplicity and feasibility—it requires minimal training, no complex equipment, and can be performed rapidly in community settings 2, 3. In under-resourced areas where measuring weight-for-height may be challenging, MUAC provides an accessible initial screening tool, with further WHZ assessment following positive screens 5.