Review Question - QID 100959

This patient's renal failure was due to ischemic acute tubular necrosis, secondary to hypovolemia. Acute tubular necrosis classically results in oliguria, "muddy brown" pigmented renal tubular cell casts as seen in Figure A, hyperkalemia, and anion gap metabolic acidosis.

Acute tubular necrosis (ATN) may be ischemic (due to hypovolemia in this case) or toxic (for example due to aminoglycosides, CT contrast, or ethylene glycol). It proceeds through an oliguric phase where GFR drops and creatinine rises, followed by a diuretic phase that subsides with tubular re-epitheliazation and regain of renal function. Treatment is largely supportive, with an immediate goal being repleting volume status, and patient should be monitored for indications for dialysis.

Simerville et al. provide a comprehensive overview of urinalysis. They note that casts in the urine are formed from Tamm-Horsfall mucoprotein and whatever else is in the tubule lumen (predominantly from the distal convoluted tubule and collecting duct). Casts may be hyaline, erythrocyte, leukocyte, epithelial, or waxy, among others, and that the type of cast is a clue to disease process. ATN produces epithelial cell casts.

Gill et al. describe patients with ATN, and note that this is one of the most common causes of acute renal failure in the hospital and its high mortality rate persists despite the availability of hemodialysis (about 36% mortality in hospitalized patients and 78% mortality in ICU patients).

Figure A shows "muddy brown" epithelial cell casts characteristic of ATN. Illustration A shows the pathophysiology of ischemia leading to ATN.

Incorrect answers:
Answer 1: Pyelonephritis would present with fever, costovertebral angle tenderness and positive urine leukocyte esterase and nitrites.
Answer 2: Diabetic glomerulopathy is a progressive renal disease due to diabetes leading to glomerulosclerosis and proteinuria, hypertension and edema.
Answer 3: Glomerulonephritis may be post-infectious and produce hematuria or proteinuria and hypertension.
Answer 5: Membranous glomerulonephritis is a commonly idiopathic autoimmune renal disease that results in nephrotic syndrome including edema, proteinuria and hyperlipidemia.