Effect of Loop Diuretics on the Fractional Excretion of Urea in Decompensated Heart Failure

Fractional Excretion of Sodium and Urea are Useful Tools in the Evaluation of AKI: CON

“…Early reports of FENa and FEUrea proposed cutoffs of FENa >3% and FEUrea >40% for attributing AKI to intrinsic renal disease but these upper limits are less often used in practice. [1][2][3][4] However, these assumptions have numerous caveats that severely limit the reliability of FENa and FEUrea to distinguish p-AKI from ATN.…”

“…10 Diuretics have been shown to alter FEUrea in hospitalized patients with hypervolemia and acute decompensated heart failure. 4 Furthermore, urea transporter expression may be influenced by volumeindependent variables, such as sepsis. 11 Even when used precisely in the intended populations, FENa and FEUrea only represent the renal handling of solute at a single time point and do not account for the dynamic nature of renal injury; serial measurements throughout the course of renal injury have been demonstrated to change substantially.…”

“…11 Even when used precisely in the intended populations, FENa and FEUrea only represent the renal handling of solute at a single time point and do not account for the dynamic nature of renal injury; serial measurements throughout the course of renal injury have been demonstrated to change substantially. 4 Furthermore, FENa and FEUrea comprise an average over the whole kidney, overshadowing variation in tubular injury. In this way, a low FENa or FEUrea could obscure tubular injury where only a subset of nephrons is affected while others remain functional.…”

Urine biochemistry assessment in the sequential evaluation of renal function: Time to think outside the box

“…Later, fractional excretion of urea (FeUr) was proposed as a better tool to identify pre-renal AKI in the context of diuretic therapy ( 12 , 13 ) due to the theoretical framework on the minor impact of diuretics on urea reabsorption. Nevertheless, this concept was lately questioned by other investigators ( 14 ).…”

Fractional Excretion of Sodium and Urea are Useful Tools in the Evaluation of AKI: COMMENTARY

“… 10 In addition, FEUrea may not be reliably <35% in congestive heart failure patients with prerenal failure receiving diuretics. 11 Instead, they propose using the findings of casts and renal tubular epithelial cells on urine microscopy now, and novel biomarkers, such as kidney injury molecule-1 (KIM-1) soon, to diagnose ATN rather than FENa and FEUrea results that may mislead the clinician.…”