Standardization of sagittal abdominal diameter measurement: protocol evaluation and diagnostic utility for central obesity compared with waist circumference

Sagittal abdominal diameter (SAD) has been proposed as an alternative or complementary measure to waist circumference (WC) for diagnosing central obesity, but standardized measurement protocols are lacking. This study aimed to establish standardized SAD protocols and validate SAD’s diagnostic performance against WC in a Chinese population. A cross-sectional study enrolled 1,881 adults in 2024. SAD was measured in both supine and standing positions at three anatomical landmarks: supine SAD1 (midpoint between the subcostal margin and iliac crest), SAD2 (umbilical level), SAD3 (the superior border of the iliac crest); and standing SAD4-6 at the corresponding landmarks. Correlations with metabolic indicators were assessed. Diagnostic performance for identifying " Two or More Nonadipose Components of metabolic syndrome (MetS) " was evaluated using ROC analysis, validated with prior data (2023, N = 701). We designed a low-cost, simple L-shaped caliper suitable for measuring SAD. Standing SAD correlated more strongly with adverse metabolic indicators than supine SAD. Among standing measurements, SAD4 and SAD5 showed the strongest correlations and highest AUCs for diagnosing central obesity. In the 2024 cohort, SAD4 and SAD5 showed slightly higher AUCs than WC in both females and males, but the differences were not statistically significant. In pooled validation with prior data, SAD5 showed slightly higher AUCs than WC in both sexes, with statistical significance observed only in males (AUC: 0.76 vs. 0.74, P = 0.03). The optimal SAD5 cutoff for diagnosing central obesity was 20.0 cm in females and 21.0 cm in males. Among Chinese adults, standing SAD measured at the midpoint between the subcostal margin and iliac crest or at the umbilical level is recommended for identifying metabolic risk factors. Compared with WC, SAD showed comparable or slightly higher diagnostic performance, and has the potential to become a simpler, novel tool for assessing obesity across various applications. Further validation in other populations is needed. Not applicable.