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Many factors may affect the reliability of impedance measurements. Whilst there are no formally accredited measurement conditions, the following commonly apply: the subject should lie supine on a non-conductive surface, limbs abducted slightly, measurements being taken 10 minutes after adopting this posture; the subject should be fasted but not dehydrated and have not undertaken, within the past 12 hours, strenous exercise, ingested alcohol or taken diuretics. The skin surface at the sites of electrode placement should be cleaned with alcohol and electrodes should be accurately placed with reference to anatomical markers.
Where careful attention has been given to subject preparation, typical coefficients of variation for within a measurement session range from 0.3 to 3%. Daily or weekly variations are greater, ranging from 1 to 5% for single frequency analysers. Reliability varies with frequency for MFBIA analysers, with coefficients of reliability greater than 95% for inter- and intra-observer differences for resistance for frequencies <500 kHz and for reactance for frequencies <100 kHz being reported. It is likely that the single largest source of error in reproducibility lies in inaccurate or variable electrode placement.