Examining within-session test-retest reliability of four bioimpedance devices among adults across a wide age range

Bioimpedance is increasingly growing in clinical utility for within-session monitoring; however, many studies neglect to report the test-retest reliability of their devices. The purpose of this study was to examine the within-session test-retest reliability of whole-body bioelectrical variables measured by four common bioimpedance devices among adults. Ninety-six adults (age = 46.1 ± 21.7yrs, female = 63.5%, BMI = 26.4 ± 5.2 kg/m²) were tested in the morning-time on each device after providing a urine sample to confirm euhydration in addition to 10 minutes of passive rest in each device's respective testing position (standing or supine). Each device assessed whole-body impedance, resistance, reactance, and phase angle in duplicate with approximately 10 seconds between trials; bioelectrical variables were extracted at 5, 50, 250, 500, and 1000 kHz as available from each device. Reliability was assessed using intraclass correlation coefficients (ICC_2,1) and coefficients of variation (CV). At 5, 50, and 250 kHz, reliability across devices and measures was excellent (ICC_2,1 > 0.90, CV = 0.78 ± 0.55%). Precision at 500 kHz for PhA (CV = 5.41%) and Xc (CV = 4.9%) was low and approaching low, respectively. Measures of Xc and PhA at higher frequencies (500 and 1000 kHz) may be less precise, but further research is needed to confirm, particularly with 1000 kHz where negative Xc values may limit the interpretability of CVs. Clinicians, researchers, and practitioners using these devices for within-session monitoring of raw bioelectrical variables should ideally test the reliability of their own devices but may use the data within this manuscript as a point of reference.