Defining Sarcopenia Using the Third Lumbar Vertebra (L3) Skeletal Muscle Index (L3SMI): Establishing Imaging Biomarker Standards for the Middle Eastern Population

This study aimed to define sarcopenia criteria using the third lumbar vertebra (L3) skeletal muscle index (L3SMI) in Middle Eastern individuals. In a retrospective review, abdominal CT imaging from 200 kidney donors was analyzed. Demographic data, BMI, body surface area, L3 skeletal muscle area (L3SMA), and L3SMI were evaluated. Mean ± SD L3SMA values were 98.63 ± 14.9 cm² for females (n = 48) and 157.52 ± 25.6 cm² for males (n = 152); corresponding L3SMI values were 40.9 ± 5.6 and 55.3 ± 8.8 cm²/m², respectively. Applying Western sarcopenia cutoffs classified 47.9% of females (n = 23/48) and 26.3% of males (n = 40/152) as sarcopenic. Defining cutoffs as two SDs below the mean yielded 29.7 cm²/m² for females and 37.7 cm²/m² for males. These gender-specific cutoffs may aid in the diagnosis of sarcopenia, support clinical risk stratification, and inform future population-based screening strategies in the Middle Eastern region. Larger multiethnic studies are warranted.