Bioelectrical Impedance Analysis Measures and Clinical Outcomes in CKD

Rationale & objective: Bioelectrical impedance analysis (BIA) provides a noninvasive assessment of body composition. BIA measures of cell integrity (phase angle) and hydration (vector length) have been associated with mortality among patients receiving dialysis. Whether these measures are associated with clinical outcomes in patients with chronic kidney disease (CKD) is unknown.

Study design: Observational study.

Settings & participants: We studied 3,751 participants with CKD in the prospective multicenter Chronic Renal Insufficiency Cohort (CRIC) who had baseline single-frequency BIA performed.

Predictors: Predictors included phase angle and vector length, which were calculated from measurements of resistance and reactance from BIA. We ranked phase angle and vector length into quartiles and compared the 2 narrower quartiles of phase angle and shorter quartiles of vector length with the 2 upper quartiles.

Outcomes: Mortality, heart failure, atherosclerotic cardiovascular disease, and progression of CKD (30% decline in estimated glomerular filtration rate or end-stage kidney disease).

Analytic approach: We tested associations of phase angle and vector length with risks for mortality and progression of CKD using Cox proportional hazard models and the association with heart failure and atherosclerotic cardiovascular disease using Fine and Gray models. All models were adjusted for demographics, comorbid conditions, and kidney function.

Results: Mean phase angle and vector length were 6.6°±1.8° and 470 ± 96 Ω/m, respectively. Relative to phase angle ≥ 6.40^o, narrower phase angle (<5.59^o) was significantly associated with mortality (HR, 1.31; 95% CI, 1.09-1.58). Relative to vector length ≥ 459 Ω/m, shorter vector length (<401 Ω/m) was significantly associated with heart failure (HR, 1.28; 95% CI, 1.01-1.61). Neither measure was associated with atherosclerotic cardiovascular disease or a composite renal end point.

Limitations: Observational study.

Conclusions: Adjusted for key confounders, BIA-derived measures of cellular integrity and tissue hydration were significantly associated with death and incident heart failure, respectively.