Changes in bioimpedance analysis components before and after hemodialysis

BACKGROUND: This study compared nutritional parameters in hemodialysis (HD) subjects and controls using bioimpedance analysis (BIA) and investigated how BIA components changed before and after HD. METHODS: This cross-sectional study included 147 subjects on maintenance HD from two hospitals and 298 propensity score-matched controls from one healthcare center. BIA was performed pre- and post-HD at mid-week dialysis sessions. RESULTS: Extracellular water/total body water (ECW/TBW) and waist-hip ratio were higher in the HD patients; the other variables were higher in the control group. The cardiothoracic ratio correlated best with overhydration (r = 0.425, P < 0.01) in HD subjects. Blood pressure, hemoglobin, creatinine, and uric acid positively correlated with the lean tissue index in controls; however, most of these nutritional markers did not show significant correlations in HD subjects. Normal hydrated weight was predicted to be higher in the pre-HD than post-HD measurements. Predicted ultrafiltration (UF) volume difference based on pre- and post-HD ECW/TBW and measured UF volume difference showed a close correlation (r(2) = 0.924, P < 0.01). Remarkably, the leg phase angle increased in the post-HD period. CONCLUSION: The estimated normal hydrated weight using ECW/TBW can be a good marker for determining dry weight. HD subjects had higher ECW/TBW but most nutritional indices were inferior to those of controls. It was possible to predict UF volume differences using BIA, but the post-HD increase in leg phase angle, a nutritional marker, must be interpreted with caution.