Hydration status assessment by multi-frequency bioimpedance in patients with advanced chronic kidney disease.

INTRODUCTION: Body composition assessment has the potential to improve the care of patients with chronic kidney disease (CKD). Whole-body multiple-frequency bioimpedance spectroscopy (BIS) appears to be a useful and appropriate technique for assessing hydration status and body composition in CKD patients.
OBJECTIVE: The aims of this study were to determine the hydration status by BIS in patients with advanced CKD, and to analyse the association of body fluid status with common clinical and biochemical characteristics. The prognostic value of the phase angle at 50 KHz (PA) was also evaluated. PATIENTS AND METHODS: The study group consisted of 175 patients (66 ± 14 year, 77 females) with eGFR < 40 ml/min not yet on dialysis. Body composition was assessed by BIS (BCM, Fresenius). Hydration status was expressed as a percentage of the total body water (TBW). Patients were prospectively followed-up for a median of 481 days, and the main determinants of mortality were estimated by Cox regression analysis.
RESULTS: The majority of patients (85%) showed a hydration status within ± 5% TBW. Patients with oedemas or uncontrolled arterial hypertension showed mean estimate fluid overload significantly higher than that of the other study patients. Fluid overload was negatively associated with serum albumin levels, body mass index and urinary sodium/potassium ratio; and positively with male gender and diabetes. During the follow-up period, 16 patients died (9%). The main determinants of mortality adjusted for other potential covariates were: Davies comorbidity index (HR = 4.304; P = .001), and PA (per each °; HR = 0.491; P = .026).
CONCLUSIONS: BIS may help identify changes in hydration status in CKD patients not fully appreciated by clinical or biochemical assessment. PA was a significant predictor of mortality in these patients.