The equivalence of hydration status measured by the Fresenius BCM and the Cella Bioimpedance Spectroscopy devices on hemodialysis patients

Background Fluid management is a serious challenge for patients undergoing hemodialysis therapy (HD). Bioimpedance spectroscopy (BIS) is a promising technique to help with clinical hydration (HYD) assessment. The Fresenius Medical Care (FMC) Body Composition Monitor (BCM) is the standard but is large and expensive. Cella Medical has introduced a small wireless BIS device. This study compared the HYD status predicted by the two devices. Methods Following the FMC BCM device manual guidelines, measurements of BIS were made wrist-ankle using typical ECG electrodes on the non-fistula side of HD patients pre dialysis while in their normal supine position. As usual, patients were measured before their normal time of therapy with the BCM. The Cella measurements were then performed within two minutes. Results Forty-two HD patients (M=64%, age=64±30 yrs.), were measured. One patient data was removed. The mean BCM HYD status was 1.86 l, SD 1.46 l, and SEM 0.22 l. Cella was 1.806 l, SD 1.36 l, and the SEM 0.21 l. The 95% difference confidence interval (CI) was -0.66 to 0.55 l. The Pearson’s correlation (r) was r^2 = 0.85 (p<0.00001). There was no proportional bias: the offset was -0.056 l, and K=1.010. The limits of agreement (LOA) analysis showed a mean difference of 0.56 l, and limits d ±2SD = (−1.192 l, 1.081 l), indicating 95% of the difference will lie within these limits. To evaluate equivalence, we performed two one-sided t-tests (TOST). When the bounds were reduced to the limit =0.47 l and -0.59 l, we obtained a 0.046 p-value (alpha =0.05), at 80% statistical power. For 26% of the subjects, the difference was <0.1 l, for 43% <0.25 l, for 71% <0.5 l, for 83% <0.75 l, for 90% <1.0 l, and for 9.5% (4 patients) more than 1 l. Only two cases (4.8%) were just over the ±2SD limit. Conclusion This study suggests the BCM and Cella devices can be used interchangeably.