Impedance ratio: a novel marker and a powerful predictor of mortality in hemodialysis patients.

Abstract

Impedance ratio (Imp-R) obtained by multifrequency bioimpedance analysis (BIA) has been shown to be associated with volume and nutrition status. In this prospective study, the predictive role of Imp-R for mortality in hemodialysis (HD) patients was investigated. Multifrequency (5-50-100-200kHz) BIA was applied to 493 prevalent HD patients in March-April 2006. Imp-R was defined as the ratio of 200-5kHz impedance values. Demographical, clinical and laboratory data at the time of the analysis were recorded. All-cause and cardiovascular (CV) mortality were assessed during 3years of follow-up. Mean age was 57.7±13.9years, HD duration 52.1±42.6months and prevalence of diabetes 21.7%. Imp-R was negatively correlated with nutritional markers including albumin, creatinine and hemoglobin levels. In addition, there was a positive correlation between Imp-R and age, ratio of extracellular water to total body water and high-sensitive C-reactive protein. Over a mean follow-up period of 27.9±11.1months, 93 deaths (52 from CV reasons) were observed. In the multivariate analysis, Imp-R was significantly associated with all-cause and CV mortality after adjustments [HR 1.13, 95% CI (1.04-1.23); p=0.004 and HR 1.15, 95% CI (1.03-1.27); p=0.01, respectively]. The risk of all-cause mortality was 3.4 times higher in the fourth quartile of Imp-R (>83.5%) compared to the first Imp-R quartile (<78.8%) as reference. Cutoff value of Imp-R for all-cause mortality was 82.0% with a sensitivity of 65.5% and specificity of 64%. Impedance ratio measured by multifrequency in standardized conditions BIA is an independent and powerful predictor of both all-cause and CV mortality in hemodialysis patients.