SHM's Clinical Quick Talks-One-Minute Guide to Fractional Excretion Indices in Acute Kidney Injury

One-Minute Guide to Fractional Excretion Indices in Acute Kidney Injury

Pdf Summary

The use of fractional excretion indices in the evaluation of acute kidney injury (AKI) is discussed in this document. Fractional excretion of sodium (FeNa) and urea (FeUrea) are urine indices that have been developed to differentiate between pre-renal azotemia and acute tubular injury/necrosis (ATI). However, the document advises against ordering urine electrolytes to calculate fractional excretion indices as part of the initial evaluation of AKI.<br /><br />The reasons for AKI can be pre-renal azotemia or ATI, and treatment approaches differ for each. Pre-renal azotemia usually requires intravascular replacement with fluids, while parenteral fluids can lead to fluid overload in ATI. Urine indices were developed to assist in differentiating between the two causes, but their usefulness has limitations.<br /><br />The document highlights that there have been studies showing a high rate of indeterminate values and misclassification due to comorbidities when using fractional excretion indices in nonoliguric patients. Additionally, the use of diuretics can cause false elevation in the indices in a pre-renal state.<br /><br />Two studies presented conflicting conclusions about the effectiveness of FeNa and FeUrea in determining AKI etiology. One study found FeUrea to be more sensitive and specific than FeNa, but it was only performed in ICU patients. Another study found FeUrea to be superior to FeNa in sensitivity only in patients taking diuretics.<br /><br />The gold standard for diagnosing the cause of AKI is to see if it resolves with fluids. A fluid challenge is often both diagnostic and therapeutic. While fractional excretion indices may be helpful in specific etiologies like hepatorenal syndrome, the document suggests that most of the time, a fluid challenge or diuresis will be the preferred diagnostic and therapeutic tests.<br /><br />In conclusion, the document advises against using fractional excretion indices in the initial evaluation of AKI. The indices have limitations and may not be accurate in all patient populations. A fluid challenge or diuresis is often the preferred approach for diagnosing and managing AKI.

Keywords

fractional excretion indices

acute kidney injury

AKI

fractional excretion of sodium

FeNa

fractional excretion of urea

FeUrea

pre-renal azotemia

acute tubular injury

necrosis