Critical Care Medicine-Renal, Electrolyte and Acid Base Disorders>>>>>Acute Renal Failure
Question 6#

A 65-year-old male admitted to the ICU with septic shock and develops nonoliguric AKI. Urinary microscopy reveals muddy brown, granular, and epithelial cell casts. Serum creatinine does not improve with fluid resuscitation. Which of the following sets of laboratory parameters is MOST consistent with a diagnosis of acute tubular necrosis?

FENa fractional excretion of sodium; Scr, serum creatinine.

A. A
B. B
C. C
D. D

Correct Answer is D

Comment:

Correct Answer: D

There are three major diagnostic approaches that are used to distinguish prerenal disease from ATN:

  1. Urinalysis: Urinalysis with sediment examination is typically normal in prerenal disease. In patients with ATN, muddy brown, granular, and epithelial cell casts are seen. Although these findings are common in ATN, they do not always indicate the presence of ATN, and conversely, their absence does not exclude ATN.
  2. Fractional excretion of sodium (FENa ): Kidneys with intact tubular function tend to conserve the sodium resulting in a low urine sodium concentration (<20 mEq/L). This is seen with the prerenal etiologies. Tubular function is impaired in ATN leading to high urine sodium concentrations (>40-50 mEq/L) as a result of defective reabsorption. FENa is not affected by urine volume and is valuable in the evaluation of AKI. FENa is typically <1% in prerenal disease and greater than 2% in patients with ATN.
  3. Response to fluid resuscitation: Response to fluid repletion is helpful to differentiate between prerenal from intrinsic renal disease. Return of the serum creatinine to previous baseline within 24 to 72 hours with fluid resuscitation most likely indicates prerenal disease, whereas persistence of AKI is most likely indicative of ATN.

References:

  1. Miller TR, Anderson RJ, Linas SL, et al. Urinary diagnostic indices in acute renal failure. Ann Intern Med. 1978;89(1):47. PMID:666184.
  2. Espinel CH, Gregory AW. Differential diagnosis of acute renal failure. Clin Nephrol. 1980;13(2):73. PMID:7363517.
  3. Perazella MA, Coca SG, Kanbay M, Brewster UC, Parikh CR. Diagnostic value of urine microscopy for differential diagnosis of acute kidney injury in hospitalized patients. Clin J Am Soc Nephrol. 2008;3(6):1615. Epub 2008 Sep 10. PMID:18784207.
  4. Steiner RW. Interpreting the fractional excretion of sodium. Am J Med. 1984;77(4):699. PMID:6486145.