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Original Article
Pediatric Nephrology
December 2009, Volume 24, Issue 12, pp 2409-2412
First online: 15 September 2009
Comparison between fractional excretions of
urea and sodium in children with acute
kidney injury
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Daryoosh Fahimi
, Saeed Mohajeri
, Niloufar Hajizadeh
, Abbas Madani
, Seyed Taher Esfahani
, Neamatollah Ataei
, Parvin Mohsseni
, Malektaj Honarmand
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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 1year 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.
Keywords
Acute kidney injury Acute renal failure Fractional excretion of sodium Fractional excretion of
urea nitrogen Intrinsic renal failure Prerenal failure Pediatrics