Reliability for multiple frequency bioelectric impedance.

Multifrequency impedance may help to quantify body fluid compartments and levels of hydration among individuals. Most studies of bioelectric impedance use impedance machines operating at a frequency of 50 kHz, and observer error is low. The present study evaluates multifrequency impedance measurements at 15 frequencies from 5 to 1,300 kHz to determine observer reliability in 20 White subjects of each sex, 18-65 years of age. Data were collected during two time periods so that a participant was measured by each of two observers during each period. There was an effect of frequency and sex on reliability. The intra- and inter-observer reliability for resistance and reactance were high with coefficients of reliability of greater than 95% at frequencies under about 500 kHz for resistance and under 100 kHz for reactance. Technical errors of measurement were generally stable across frequencies for resistance but became increasingly large above 100 kHz for reactance. Resistance measures of men were more reliable than those of women. Reliability was reduced at high frequencies which are potentially useful in determining body fluid volumes. There was no effect of age on reliability. © 1994 Wiley-Liss, Inc.