Norms and correlates of bioimpedance phase angle in healthy human subjects, hospitalized patients, and patients with liver cirrhosis

Abstract

This study investigates whether bioimpedance indexes rather than derived body compartments would be adequate for nutritional assessment. Evidence is provided that the phase angle as determined by conventional tetrapolar whole body bioelectrical impedance analysis at 50 kHz (1) was largely determined by the arms and legs and not the trunk, (2) was higher in control subjects than in hospitalized patients [mean (SD) 6.6 degrees (0.6) degrees vs 4.9 degrees (1.2) degrees, P<0.001], (3) discriminated poorly between cirrhotic patients of different Child-Pugh class, and (4) was positively correlated with muscle mass ( r=0.53) and muscle strength ( r=0.53) in these patients (each P<0.01). In a prospective study of patients with liver cirrhosis Kaplan-Meier and log rank analyses of survival curves demonstrated that patients with phase angles equal to or less than 5.4 degrees had shorter survival times than patients with higher phase angles [6.6 degrees (1.4) degrees ] and that phase angles less than 4.4 degrees were associated with even shorter survival times ( P<0.01). The prognostic roles of the phase angle and standard nutritional parameters such as total body potassium, anthropometric measurements, and impedance derived fat free mass, body cell mass and fat mass were evaluated separately by Cox regression which eliminated all variables except the phase angle as predictors of patient survival time ( P<0.01). We concluded that for the clinical assessment of patients the phase angle may be superior to commonly used body composition information.