You are asked to consult on a previously healthy 68-year-old woman who presented with malaise and one episode of hematuria. She visited her primary care doctor 5 days ago for a “bladder infection” and was prescribed trimethoprim-sulfamethoxazole, which she has been taking. She is alert and oriented, and her physical examination is within normal limits. Her vital signs are normal. Her laboratory data are unremarkable except for elevated eosinophils, creatinine of 3 mg/dL, and urea 41 mg/dL.
What would you expect to see in urine analysis?A. Muddy brown cast
Correct Answer: C
Acute interstitial nephritis (AIN) is a rare cause of AKI. Most patients present with nonspecific signs and symptoms of acute kidney failure. The classical triad of fever, rash, and eosinophilia occurs only in 10% of the population. Moreover, patients can be oliguric or nonoliguric, and hematuria can occur in 5% of them. The most common cause of AIN is drug-associated, such as trimethoprim-sulfamethoxazole that the patient has been taking. Other causes include infection, idiopathic, or associated with systemic autoimmune diseases. Laboratory results usually show an increase in creatinine level, eosinophilia or eosinophiluria, white blood cells or white blood cell casts in urine (question 1—choice C), and a variable degree of proteinuria.
Muddy brown cast is usually seen in acute tubular necrosis (ATN), which is associated with prolonged prerenal insult or nephrotoxin induced. Red blood cell cast is associated with acute glomerulonephritis, in which immunological mechanisms cause glomerular inflammation. These mechanisms could be infection-related, cancer, or exposure to drugs of toxins. Enveloplike, calcium oxalate crystals are seen in patients with ethylene glycol poisoning. As the patient is healthy and does not have any risk factors, and her examination is normal, ATN, acute glomerulonephritis, or ethylene glycol poisoning are very unlikely.