ACCURACY OF BIOELECTRICAL-IMPEDANCE ANALYSIS IN ESTIMATION OF EXTRACELLULAR-SPACE IN HEALTHY-SUBJECTS AND IN FLUID RETENTION STATES

Bioelectrical impedance analysis (BIA) is a noninvasive method recentl y introduced for body fluid evaluation in healthy subjects. The purpos e of this paper is to verify the reliability of bioelectrical measurem ents in extracellular water (ECW) prediction in healthy subjects and i n fluid retention states. We studied 40 subjects (19 males and 21 fema les) aged 21-81 years; 22 were healthy subjects, 12 were affected by c hronic heart failure, and 6 by chronic renal failure. In all subjects resistance (R) and reactance (Xc) at 1 and 50 kHz corrected for height were compared with ECW measured by the bromide dilution method. Our r esults suggested a different behavior of the current in fluid-retentio n states with respect to healthy subjects. ECW was best predicted by r esistance at 1 kHz corrected for height, group (considered as dummy va riable), weight and gender (R(2) = 0.89, p < 0.001, SEE = 1.7 liters). The bioelectrical impedance analysis at 50 kHz explained the 89 % of ECW variability when resistance and reactance corrected for height are considered with gender group and weight (R(2) = 0.89, p < 0.001, SEE = 1.7 liters). In conclusion, the bioelectrical method at 1 kHz can be considered sufficiently accurate in ECW prediction in healthy subject s and in fluid retention states. Also, the bioelectrical impedance ana lysis at 50 kHz is useful for predicting ECW, but his role must be fur ther investigated.