Egyptian Journal of Critical Care Medicine (Apr 2013)

Comparison between fractional excretion of sodium and fractional excretion of urea in differentiating prerenal from renal azotemia in circulatory shock

  • Abdel Rahman Yassin,
  • Hossam M. Sherif,
  • Ahmed Yehia Mousa,
  • Amr Esmat

DOI
https://doi.org/10.1016/j.ejccm.2013.05.001
Journal volume & issue
Vol. 1, no. 2
pp. 69 – 77

Abstract

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Background: Fractional excretion of sodium (FENa) is used to differentiate renal from prerenal azotemia. However, many drugs and medical conditions affect the sodium (Na+) handling in the kidney. But the fractional excretion of urea (FEurea) is dependent on passive forces and is less influenced by the diuretic therapy. Objective: Comparison between FENa and FEurea in differentiating renal from prerenal azotemia in circulatory shock, and the effect of diuretics on their handling. Methods: Both FENa and FEurea were measured in 40 patients (pts) with AKI complicating circulatory shock. The pts were divided into 26 pts with prerenal (group-1) and 14 pts with renal azotemia (group-2). Group-1 was subdivided into 12 pts who did not receive diuretics 24 h before the sampling process (group-1a) and 14 pts who received diuretics (group-1b). Results: Compared to patients with renal azotemia (group-2), those with prerenal azotemia (group-1) showed significantly lower FENa (0.99 ± 0.66 and 2.57 ± 1.73, P < 0.05) respectively, and significantly lower FEurea (29.7 ± 7.6 and 43.7 ± 15.4, P < 0.001) respectively. For differentiating renal from prerenal azotemia, compared to FENa, FEurea showed better sensitivity (78.1% vs. 71.4%) and specificity (88.5% vs. 69.4%) respectively. Moreover, FEurea was not significantly affected by the use of diuretics; sensitivity (78% vs. 78%) and specificity (92% vs. 88%) respectively, compared to pts who did not receive diuretics. On the other hand, compared to pts who did not receive diuretics, the use of diuretics significantly affected FENa; sensitivity (64% vs. 71%) and specificity (58% vs. 70%) respectively. Conclusions: FEurea is more sensitive, specific and less affected by the use of diuretics than FENa in differentiating renal from prerenal azotemia in patients with AKI complicating circulatory shock.

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