Electrolyte Disorders USMLE Step 1 Practice Question
A 46-year-old man with crush injury is admitted after being trapped under debris for several hours. He has dark urine and severe muscle pain. Laboratory studies show potassium 7.4 mEq/L, calcium 7.4 mg/dL, phosphate 6.9 mg/dL, creatine kinase markedly elevated, and creatinine 2.9 mg/dL. Which of the following best explains the low calcium level in this patient?
Answer choices
- AIncreased distal nephron calcium excretion due to thiazide therapy
- BLoss of PTH due to pituitary dysfunction
- CReduced albumin synthesis from cirrhosis
- DExcess calcitonin release from the thyroid
- ECalcium deposition in damaged muscle and binding by released phosphateCorrect answer
- FDecreased production of calcitriol by damaged kidneys with impaired 1α-hydroxylase activity
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