Utility of fractional excretion of urea nitrogen in heart failure patients with chronic kidney disease

AIMS: Maintenance of euvolaemia with diuretics is critical in heart failure (HF) patients with chronic kidney disease (CKD); however, it is challenging because no reliable marker of volume status exists. Fractional excretion of urea nitrogen (FEUN) is a useful index of volume status in patients with renal failure. We aimed to examine whether FEUN is a surrogate marker of volume status for risk stratification in HF patients with CKD. METHODS AND RESULTS: We examined 516 HF patients with CKD (defined as discharge estimated glomerular filtration rate < 60 mL/min/1.73 m(2)) whose FEUN was measured at discharge (median age, 80 years; 58% male). The patients were divided into four groups according to quartile FEUN value at discharge: low‐FEUN, FEUN ≤ 32.1; medium‐FEUN, 32.1 < FEUN ≤ 38.0; high‐FEUN, 38.0 < FEUN ≤ 43.7; and extremely‐high‐FEUN, FEUN > 43.7. FEUN was calculated by the following formula: (urinary urea × serum creatinine) × 100/(serum urea × urinary creatinine). During the 3 year follow‐up, 131 HF readmissions occurred. Kaplan–Meier analysis showed that the HF readmission rate was significantly lower in the medium‐FEUN group than in the other three groups (log‐rank test, P = 0.029). Multivariate Cox regression analysis identified the low‐FEUN, high‐FEUN, and extremely‐high‐FEUN values as independent factors associated with post‐discharge HF readmission. In the analysis of 130 patients who underwent right heart catheterization during hospitalization, a significant correlation between FEUN value and right atrial pressure was observed (R = 0.243, P = 0.005). Multivariate linear regression analysis revealed that FEUN value at discharge decreased in a dose‐dependent manner with loop diuretics. CONCLUSIONS: In HF patients with CKD, FEUN is a potential marker of volume status for risk stratification of post‐discharge HF readmission. Low FEUN value (FEUN ≤ 32.1) may represent intravascular dehydration, whereas high FEUN value (FEUN > 38.0) may represent residual congestion; both of them were independent risk factors for HF readmission. FEUN may be useful to determine euvolaemia and guide fluid management in HF patients with CKD.