Definition

• Oliguric: Anuria or oliguria (<0.5 mL/kg/h in children; <1 mL/kg/h in infants) with an associated increase in serum creatinine
  
• Non-oliguric: Increased serum creatinine with normal or increased urine output (usually seen with nephrotoxic medications)

Etiology

• It should be understood that the following classifications of etiology are somewhat artificial because there can be a great deal of overlap (eg, sepsis can cause both prerenal and intrinsic renal disease; obstructive uropathy, if severe enough, can also cause intrinsic renal disease).

Diagnosis

• Perform history to elicit predisposing factors listed above and physical exam to palpate for abdominal masses and other congenital urogenital abnormalities.
  
• Bladder catheterization to confirm inadequate urine output and r/o obstruction.
  
• If prerenal failure is suspected on the basis of history or physical exam and there is no evidence of heart failure or volume overload, a fluid challenge of 10–20 mL/kg of normal saline can be administered over 30–60 min. Lack of response suggests intrinsic renal or postrenal failure.
  
• Laboratory studies
  
  
  
  • Serum electrolytes, BUN, creatinine
    
  • CBC, platelet count
    
  • Urinalysis with microscopic analysis
    
  • Urinary sodium and creatinine with simultaneous serum sodium and creatinine to calculate FENa (these studies are not valid if diuretic is used)

• Imaging: US examination of kidneys and urinary system