Comparison of body composition assessment across body mass index categories by two multifrequency bioelectrical impedance analysis devices and dual-energy X-ray absorptiometry in clinical settings

Background: InBody-770 and SECA mBCA 515 are multifrequency bioelectrical impedance analysis (BIA) devices, which are commonly used in the clinic to assess fat-free mass (FFM) and body fat (BF). However, the accuracy between devices in clinical settings, across different body mass index (BMI) groups remains unclear. Methods: Body composition for 226 participants (51% men, aged 18–80 years, BMI 18–56 kg/m²) was assessed by two commercial multifrequency BIA devices requiring standing position and using eight-contact electrodes, InBody 770 and SECA mBCA 515, and compared to results from dual-energy X-ray absorptiometry (DXA). Measurements were performed in a random order, after a 3 h fast and no prior exercise. Lin’s-concordance correlation and Bland–Altman analyses were used to compare between devices, and linear regression to assess accuracy in BF% across BMI groups. Results: We found strong correlation between DXA results for study population BF% and those obtained by InBody (ρ_c = 0.922, 95% confidence interval (CI) 0.902, 0.938) and DXA and SECA (ρ_c = 0.940, CI 0.923, 0.935), with 95% limits of agreements between 2.6 and −8.9, and 7.1 and −7.6, respectively. BF% assessment by SECA was similar to DXA (−0.3%, p = 0.267), and underestimated by InBody (−3.1%, p < 0.0001). InBody deviations were largest among normal weight people and decreased with increasing BMI group, while SECA measurements remained unaffected. Conclusions: Both BIA devices agreed well with BF% assessment obtained by DXA. Unlike SECA, InBody underestimated BF% in both genders and was influenced by BMI categories. Therefore, in clinical settings, individual assessment of BF% should be taken with caution.