Impedance-derived phase angle as an indicator of physical function in maintenance hemodialysis patients

Maintenance hemodialysis (MHD) patients often impairs physical function, leading to reduced quality of life and increased mortality. Phase angle (PhA), derived by bioelectrical impedance analysis, has been proposed as a predictor of sarcopenia, holds promise as a potential indicator of physical function. The aim of this study was to identify the association between PhA and physical function in MHD patients.

This was a multicenter, cross-sectional study included MHD patients from seven dialysis centers from 2020 to 2021. Physical function was measured by handgrip strength (HGS), Short Physical Performance Battery (SPPB), 4-meter gait speed, and timed up and go test (TUGT). Nutritional status was assessed by malnutrition inflammation score (MIS). Body composition, including PhA at 50kHz, was measured by bioelectrical impedance analysis. Sarcopenia was diagnosed according to the 2019 update version of the Asian Working Group for Sarcopenia. Multivariable linear regression models were performed to determine the association between PhA and physical function.

A total of 864 patients (61% male, median age 63 years) were analyzed. The median PhA was 4.5 (interquartile range: 3.9-5.2)°. PhA was negatively associated with age, MIS, Charlson comorbidity index, extracellular water/total body water, visceral fat area, and TUGT, and positively associated with hemoglobin, serum albumin, body mass index, height, weight, skeletal muscle mass index (SMI), SPPB, 4-meter gait speed, and HGS. These associations were consistent across PhA values of whole body and five body segments-right arm, left arm, trunk, right leg, and left leg. Multivariable linear regression analyses indicated that PhA was independently associated with higher SPPB scores (β = 0.33, P < 0.001), faster gait speed (β = 0.29, P < 0.001), greater HGS (β = 0.28, P < 0.001) and shorter TUGT time (β = -0.20, P < 0.001) after fully adjusted for age, sex, spKt/V, dialysis vintage, Charlson comorbidity index, MIS and skeletal muscle index. Subgroup analyses confirmed the robust association of PhA with physical function across different patient characteristics including sarcopenia, malnutrition, age, sex, and diabetes.

Higher PhA was independently associated with better physical function in MHD patients. Our study suggested that PhA may serve as a non-invasive, reliable clinical indicator for assessing functional status in this population.