P522 - NOVEL BIOELECTRICAL IMPEDANCE EQUATION TO ESTIMATE SKELETAL MUSCLE FROM COMPUTED TOMOGRAPHY

P522

NOVEL BIOELECTRICAL IMPEDANCE EQUATION TO ESTIMATE SKELETAL MUSCLE FROM COMPUTED TOMOGRAPHY

A. P. T. Fayh^1,2,*, A. D. S. Rebouças¹, C. M. Prado³, M. C. Gonzalez⁴, J. P. Costa-Pereira⁵

¹Universidade Federal do Rio Grande do Norte , Natal, ²Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, Brazil, ³Human Nutrition Research Unit, University of Alberta, Edmonton, Canada, ⁴Universidade Federal de Pelotas, Pelotas, ⁵Universidade Federal de Pernambuco, Recife, Brazil

Rationale: Bioelectrical impedance analysis (BIA) requires validated equations tailored to specific populations and devices to estimate body composition. In this study, we aimed to develop a predictive equation for BIA to evaluate skeletal muscle area (SMA in cm²) using computed tomography (CT) as the reference method.

Methods: It is a cross-sectional, bi-center study, involving 211 patients with colorectal cancer for convenience. BIA was conducted using a tetrapolar model, measuring resistance (R), and reactance (Xc) values. CT scans was the reference standard technique for assessing SMA. The equation was developed using a linear regression model, maintaining variables that best correlate to SMA from CT. Internal validity was assessed using Bland-Altman plots and bootstrapping resampling method. Lins’ concordance correlation coefficient (CCC), root mean squared error (RMSE), and mean absolute error (MAE) were calculated before and after resampling.

Results: The proposed equation was as follows: SMA_BIA (cm²) = 100.401 – (0.329 x age) – (21.246 x sex) + (0.545 x weight) + (30.052 x height) - (0.126 x resistance) + (0.642 x reactance). This model accounted for more than 85% of the variability in SMA from CT (R² _adjusted = 0.86), with a RMSE of 10.37 cm² and MAE of 8.28 cm². SMA-BIA was highly correlated with SMA-CT (ρ = 0.93, P < .001). Bland-Altman plots and CCC (0.92) demonstrated a moderate agreement between them. Bootstrap analyses based on a sample of 10,000 further demonstrated the equation's validity, yielding a lower RMSE (10.31 cm²).

Conclusion: Despite methodological challenges and a relatively high (but acceptable) error, the newly proposed BIA equation demonstrated potential for predicting SMA-CT as the reference standard. Our hypothesis requires further investigation in both healthy and clinical populations.

Disclosure of Interest: None declared