Background: The role of multifrequency bioimpedance(MF-BIA) in the assessment of fluid status in dialysis patients is still not fully elucidated. Especially, the predictive value of reference values for extracellular water (ECW) has not yet been addressed. Aim of the present study was to validate cut-off values for MF-BIA in the diagnosis of hypervolemia in dialysis patients, using strict clinical criteria and echocardiography as reference techniques.
Methods: 90 patients [42 on hemodialysis; 48 on peritoneal dialysis] were divided into the following groups: clinically normovolemic (mean 24- or 48-hour systolic blood pressure below 133 mm Hg without use of antihypertensive agents; n = 12), 'hypervolemic' (mean systolic blood pressure above 133 mm Hg with 2 or more antihypertensive agents; n = 34) or undetermined (n = 44). The 80th percentile for normalized ECW in the clinically normovolemic patients was used as reference value. 20 healthy age-matched controls were included for comparison.
Results: The 80th percentiles for ECW:body weight (BW) and ECW:height in 'normovolemic' subjects were, respectively, 0.245 liters/kg and 10.96 liters/m in males, and 0.232 liters/kg and 9.13 liters/m in females. ECW:BW and ECW:height were above these values in, respectively, 26 (sensitivity 76%) and 29 (sensitivity 86%) of the 34 'hypervolemic' patients. In the undetermined group, left ventricular end-diastolic diameter was significantly different between patients with normalized ECW below and above these cut-off values (49.0 +/- 5.1 vs. 52.4 +/- 5.7 mm; p < 0.05). Use of the ECW:TBW ratio resulted yielded low sensitivity (45%). ECW:height was lower in the 'normovolemic' dialysis patients compared to healthy controls (9.7 +/- 1.3 l/m versus 12.2 +/- 1.9 l/m).
Conclusion: In our study population, ECW by MF-BIA, normalized for height was able to predict hypervolemia, based on strict clinical criteria, with a sensitivity of 86% and a specificity of 80%. The normalization procedure for ECW may influence the classification of hydration status. Strictly normotensive dialysis patients had lower normalized ECW than healthy control subjects.