Nutritional and prognostic correlates of bioimpedance indexes in hemodialysis patients

Abstract

We carried out a cross sectional and longitudinal study to assess whether bioimpedance indexes (resistance, Rz; reactance, Xc; phase angle, PA) reflect the nutritional status of hemodialysis (HD) patients, and bear a significant association with their long-term survival. The bioimpedance data of 131 patients on chronic HD treatment were compared with those of 272 healthy controls matched for age and sex. Nutritional status was assessed by anthropometric variables, serum albumin (SA), normalized protein catabolic rate (nPCR), and subjective global assessment (SGA). All three bioimpedance indexes varied significantly with HD treatment, however, with the exception of Xc in post-HD, they were on average significantly (P < 0.016) different from controls either pre- and post-HD. Post-HD PA appeared to be the best index of nutritional status, being significantly correlated with SA, age, mid arm muscle circumference (MAMC), SGA, and nPCR (R2 = 0.44; P < 0.01). However, depending on the cut-off levels, PA failed to detect clinically overt malnutrition in one to two thirds of the patients with the worst SGA score. During the follow-up the changes in bioimpedance indexes reflected poorly the changes in dry blood weight, only delta Rz bore a significant correlation (r = 0.29; P < 0.01) with delta body wt. Patients having baseline phase angle values within the lower quartile had a significantly lower two-year survival rate than patients having higher values (59.3% vs. 91.3%; P < 0.01). Cox's analysis (proportional hazard model) showed that phase angle as a predictor of death outweighed all other parameters included in the model (age, SA, nPCR, MAMC, SGA), with a relative risk of 2.6 (95% CI = 1.6 to 4.2). Bioimpedance indexes do not appear to be reliable in detecting clinically overt depletion of lean body mass. However, the strong association of PA with patient survival suggests that this bioimpedance index reflects some dimension of the illness, which is not fully identifiable with the deranged nutritional status.

Phase angle and World Health Organization criteria for the assessment of nutritional status in children with osteogenesis imperfecta

“…The PA has been used as a marker of nutritional status in clinical practice of adults6 - 9 and children13 and, when associated with anthropometric data of weight and height in patients at nutritional risk, it is a good screening tool.…”

“…This was a secondary analysis of the study on the prevalence of malnutrition in HCFMRP-USP carried out in 2013 9. The study was approved by Institutional Review Board of HCFMRP-USP.…”

“…Its use has been recommended as an indicator of prognosis in clinical practice. In adults, positive associations have been found between PA and survival of HIV-positive patients,6 , 7 and those with pulmonary cancer,8 as well as sepsis and those undergoing hemodialysis 9…”

Abnormalities of bioimpedance measures in overweight and obese hemodialyzed patients

“…20 Furthermore, this technique allows an early detection of abnormal nutritional status in physiological conditions as well as in a variety of pathological conditions, including uremia. 21 ± 26 In particular, the alterations of PA, which is an independent predictor of death in uremic patients, 25,27,28 precede the changes of biochemical nutritional parameters. 25 The current study was designed to gain insights into the in¯uence of body size, as indicated by body mass index, upon body composition in hemodialysis patients.…”

“…21 ± 26 In particular, the alterations of PA, which is an independent predictor of death in uremic patients, 25,27,28 precede the changes of biochemical nutritional parameters. 25 The current study was designed to gain insights into the in¯uence of body size, as indicated by body mass index, upon body composition in hemodialysis patients. To this aim, we performed bioimpedance analysis and anthropometry in groups of patients with different BMI.…”