Comparison between fractional excretions of urea and sodium in children with acute kidney injury

Abstract

Fractional excretion of sodium (FENa) has been said to be the most sensitive index for differentiating prerenal failure (PRF) from intrinsic renal failure (IRF). However, there are several instances of high FENa (>2%) in cases of PRF and low FENa (<1%) in IRF patients. In contrast, the fractional excretion of urea nitrogen (FEUN) is primarily dependent on passive forces, and many confounding variables that affect FENa have little effect on FEUN, if any. To compare FEUN with FENa, pediatric patients with acute kidney injury (AKI) were prospectively evaluated by history, physical examination, and obtaining appropriate laboratory data during a 1-year interval. Diagnosis of PRF or IRF was made in each patient, and renal failure indices were compared between two groups using chi-square and t test, as appropriate. Probability value (P value) <0.05 was considered significant. Receiver operating characteristic (ROC) plots for FEUN and FENa were drawn to compare the discriminative power of each index. Forty-three patients were enrolled in the study. There were 27 patients in the PRF and 16 in the IRF group. FENa was 2+/-0.4 in PRF and 4.5+/- 1% in IRF patients (P<0.05), and low FENa (<1%) was only seen in 44.4% of PRF patients, which was not statistically different from those with IRF (P>0.05). FEUN was 23.6+/- 4.9% in PRF and 41.6+/-4.8% in IRF patients (P<0.05), and low FEUN (<35%) was seen in 77.8% of the PRF group (P<0.05). Cutoff values of 30% and 1.6% were reached for FEUN and FENa, respectively. In conclusion, FEUN <35% had higher sensitivity and specificity than FENa <1% for differentiation of PRF from IRF.

Comparison of clinical and biochemical markers of dehydration with the clinical dehydration scale in children: a case comparison trial

“…The current study also confirmed more urea in our patients, although the degree of change was modest and not clinically significant. Surprisingly, the present study did not demonstrate a significant association between the fractional urea excretion [23] that is rarely studied in children in this setting.…”

Urinary Biomarkers in the Clinical Prognosis and Early Detection of Acute Kidney Injury

“…Similarly, diagnostic mainstays of AKI evaluation such as the fractional excretion of sodium (FENa) have long been shown to be suboptimal tools in the complex setting of cardiac surgery AKI (24), in which volume status, fluid responsiveness, and diuretic use confound inferences regarding the relationship between tubular function and injury (26,27). Additionally, although recent data support the utility of the fractional excretion of urea (FEUrea) as a diagnostic tool in AKI (28), not all data support its use (29). Furthermore, very little is known about the utility of FENa or FEUrea compared with the novel urinary biomarkers discussed above for the differential diagnosis and prognostic evaluation of AKI.…”

The kidney speaks: interpreting urinary sodium and osmolality

“…Other studies, however, questioned the utility of urine electrolytes. For instance, some studies question the reliability of FENa or failed to identify a correlation between FENa and spontaneous recovery of renal function 14–16. However, there is a serious problem with all these studies: there is no gold standard to distinguish between prerenal failure and AKI against which the utility of urinary indices could be assessed.…”