Generalizability of extracellular-to-intracellular fluid ratio using bio-impedance spectroscopy

Generalizability theory was used to investigate the score consistency of observed extracellular fluid/intracellular fluid (ECF/ICF) ratio measurements for both the global and leg-segmental bio-impedance spectroscopy methods. The test instrument used was a Xitron Hydra ECF/ICF Bio-Impedance Analyzer System, model 4200 (Xitron Technologies, San Diego, CA). Fifty able-bodied American men (17 to 72 years) and 50 able-bodied American women (17 to 76 years) volunteered as experimental subjects. Xitron continuous global and leg-segmental ECF/ICF procedures for testing were followed for assessing subjects in both the standing erect and lying supine postures. A two-facet, person-by-trial, completely crossed design was used, and all facets were treated as random. Data were independently analyzed for each method, each body posture and each sex group. The major findings of this study were: (1) the leg-segmental method was superior in producing the higher G-coefficients when compared to the global method regardless of gender or posture; (2) the global method resulted in higher G-coefficients in males compared to females regardless of posture; (3) when the global method was used, the relative and absolute error variances were higher for females while the opposite trend was observed when the segmental method was used and (4) when using the global method, the precision of the ECF/ICF ratio scores in females could be increased by simply using the mean of several trials (e.g., by using the mean of 5, 10 or more test trials).