A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 21-year-old man is brought to the emergency department 30 minutes after being found unconscious in his apartment by his mother. On arrival, he is unable to provide history. The mother reports that there is no history of serious illness in the family. The patient appears drowsy and dehydrated. His temperature is 38.5°C (101.3°F), pulse is 110/min, and blood pressure is 170/100 mm Hg. Examination shows several track marks on his forearms and large contusions over his forehead, legs, and back. There is blood coming from the mouth. The patient is catheterized and tea-colored urine is drained. Urinalysis shows:
Urine
pH 5.8
Specific gravity 1.045
Blood 3+
Glucose 3+
Proteins 1+
Ketones 1+
RBC none
WBC 0-1/hpf
Urine toxicology is positive for opiates and cocaine. Intravenous fluids and sodium nitroprusside drip are started. The patient is most likely to have which of the following?"
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A
Low serum potassiumIncorrect. Hyperkalemia, not hypokalemia, is expected because K+ is released from injured myocytes and worsens as renal function declines.
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B
Low blood urea nitrogenIncorrect. BUN is typically elevated, not low, due to myoglobin-induced acute tubular necrosis.
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C
Elevated serum calciumIncorrect. Calcium is usually low in rhabdomyolysis because Ca2+ precipitates with phosphate in damaged muscle; rebound hypercalcemia can occur late in recovery but not at presentation.
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D
Elevated serum creatine kinaseCorrect. Massive skeletal muscle breakdown from cocaine toxicity, prolonged immobilization, and trauma releases CK into the serum, often >5× normal, and is the hallmark lab finding of rhabdomyolysis.
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E
Low serum phosphateIncorrect. Hyperphosphatemia, not hypophosphatemia, is expected in rhabdomyolysis because phosphate is released from injured myocytes and further accumulates as renal function declines.
↑ Tap an answer to reveal the reasoning
Answer: D. A young man found unconscious with track marks, multiple contusions, hyperthermia, hypertension, and tea-colored urine that dips strongly positive for blood but shows no RBCs on microscopy has rhabdomyolysis, almost certainly from cocaine and opiate intoxication with prolonged immobilization. The urine dipstick reaction is positive because it detects heme groups — it cannot distinguish hemoglobin from myoglobin — so myoglobinuria from muscle breakdown gives a 'blood positive, RBC negative' pattern.
Massive skeletal muscle injury releases creatine kinase (CK), myoglobin, potassium, phosphate, and uric acid into the circulation. Serum CK is the most sensitive and specific marker, typically rising more than 5× the upper limit of normal and often into the tens of thousands. Hyperkalemia (not hypokalemia) is expected because of intracellular K+ release; hypocalcemia is common as calcium deposits in damaged muscle. BUN typically rises with acute kidney injury from myoglobin-induced tubular toxicity, and glycosuria here reflects proximal tubular damage rather than hyperglycemia.
Management is aggressive IV fluid resuscitation to maintain urine output >200–300 mL/h, with consideration of sodium bicarbonate to alkalinize the urine. The cocaine-induced hypertension is being managed with nitroprusside.
**Why each option:**
**A.** Hyperkalemia, not hypokalemia, is expected because K+ is released from injured myocytes and worsens as renal function declines.
**B.** BUN is typically elevated, not low, due to myoglobin-induced acute tubular necrosis.
**C.** Calcium is usually low in rhabdomyolysis because Ca2+ precipitates with phosphate in damaged muscle; rebound hypercalcemia can occur late in recovery but not at presentation.
**D.** Correct. Massive skeletal muscle breakdown from cocaine toxicity, prolonged immobilization, and trauma releases CK into the serum, often >5× normal, and is the hallmark lab finding of rhabdomyolysis.