Agreement of wearable and standing bioimpedance devices with bioimpedance spectroscopy estimates of total body water in adults with Down syndrome

Background Wearable bioimpedance technology offers a potentially accessible method for assessing total body water (TBW), yet its agreement with laboratory-based approaches in adults with Down syndrome remains unclear. The purpose of this study was to evaluate whether a wearable bioimpedance device demonstrates agreement with laboratory-based bioelectrical impedance spectroscopy (BIS) estimates of TBW comparable to standing bioimpedance devices in adults with Down syndrome. Methods Sixteen adults with Down syndrome (age: 28.3 ± 9.2 year; height: 150.9 ± 7.8 cm; body mass: 77.4 ± 20.3 kg) completed TBW assessment using BIS (reference), a wearable bioimpedance device (BIA W ), and two standing multi-frequency bioimpedance analyzers (BIA ST1 , BIA ST2 ). Results Repeated measures ANOVA revealed significant differences among devices (F (3,42) = 17.52, p < 0.001). Both standing devices produced lower TBW values compared with BIS (p < 0.001; d = 1.32 and 1.00), whereas BIA W did not differ from BIS (p = 0.106; d = 0.45). All devices demonstrated strong correlations with BIS (r = 0.92–0.93). Bland–Altman analyses showed systematic underestimation for standing devices (− 3.12 ± 4.65 L and − 2.36 ± 4.64 L), while the wearable exhibited the smallest bias (− 1.07 ± 4.64 L). Standard error of estimate values were similar across devices (2.34–2.45 L). Conclusion These findings indicate that wearable bioimpedance technology demonstrated closer agreement with laboratory-based TBW estimates than standing devices.