Beyond Body Mass Index: Accurate Metabolic Disease-Risk Phenotyping With 3D Smartphone Application.

Objective: Smartphone applications (apps) with optical imaging capabilities are transforming the field of physical anthropometry; digital measurements of body size and shape in clinical settings are increasingly feasible. Currently available apps are usually designed around the capture of two-dimensional images that are then transformed with app software to three-dimensional (3D) avatars that can be used for digital anthropometry. The aim of the current study was to compare waist circumference (WC), hip circumference (HC), four other circumferences (right/left upper arm, thigh) and WC/HC evaluated with a novel high-precision 3D smartphone app to ground-truth measurements made with a flexible tape by a trained anthropometrist.

Methods: Forty-four participants aged 20-78 years and body mass index 18.5-48.5 kg/m² completed digital and manual circumference evaluations and dual-energy X-ray absorptiometry for visceral adipose tissue mass (VAT).

Results: 3D-digital and ground-truth tape WC, HC, and WC/HC estimates were highly correlated (R ²s, 0.90-0.97, p < 0.001), mean 3D and tape group means at each site did not differ significantly, mean absolute (± SD) and root-mean square errors were low (e.g., WC, 3.4 ± 2.6 and 4.4 cm), and strong concordance correlations were present (0.90-0.99); bias with Bland-Altman analyses was small but significant (p < 0.001) for WC and WC/HC. Comparable results were observed for the four other circumferences. VAT was equally well-correlated with 3D and tape WC measurements (R ²s 0.70, 0.69, both p < 0.001); comparable tape-3D VAT-WC/HC associations were also observed in males (R ²s, 0.85, 0.73, both p < 0.001) and females (R ²s, 0.43, p < 0.01; 0.73, p < 0.001).

Conclusions: Digital anthropometry, with accessible technology such as the evaluated novel 3D app, has reached a sufficiently developed stage to go beyond body mass index for phenotyping patient's metabolic disease risks.