USMLE® Step 1 & 2

Kaplan USMLE Step 2: What do these lab studies reveal?


If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

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An 81-year-old man is brought to the hospital after being found on his living room floor. He had last been in contact with his family three days ago. While he is obtunded, he is breathing on his own and is hemodynamically stable.

His physical examination is significant for a temperature of 38 ºC (100.7 ºF) and a tender, tense right calf, thigh and buttock. His laboratory studies show:

  • Potassium—5.9 mEq/L.
  • Serum Creatinine—3.5 mg/dL.
  • Lactic Acid—2.6 mmol/L.
  • Serum Creatine Kinase—7,200 U/L.
  • White Blood Cells—17,000/mcL.
  • BUN—88 mg/dL.

Which of the following is the most appropriate management of this patient's condition?

A. Emergency fasciotomy.

B. IV mannitol.

C. IV sodium bicarbonate.

D. Oral Kayexalate.

E. Urgent hemodialysis.

F. Vascular surgical consult for creation of an arteriovenous fistula.












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The correct answer is E.

This patient presents with elevated levels of the skeletal muscle isoenzyme serum creatinine phosphokinase and myoglobin, which is suggestive of muscle injury and rhabdomyolysis. Skeletal muscle injury causes the release of muscle contents into the serum including potassium and myoglobin that can result in acute kidney injury. The most appropriate management of this patient’s condition is urgent hemodialysis to protect the kidney and reduce the risks of hyperkalemia-induced complications.

Choice A: Emergent fasciotomy is designed to release pressure and prevent damage to tissues caused by the swelling of the necrotic muscle. Although this may be necessary, correction of his hyperkalemia is more important at this point. 



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