Calcium and Parathyroid USMLE Step 1 Practice Question
A 35-year-old woman with pulmonary sarcoidosis presents with flank pain and hematuria. Vital signs: BP 128/82, HR 88, RR 16, Temp 37.2°C, SpO2 98%. Labs reveal serum calcium 11.2 mg/dL (normal 8.5-10.5), PTH 15 pg/mL (suppressed), and 1,25-dihydroxyvitamin D 89 pg/mL (elevated). Urine culture is negative. CT abdomen confirms nephrolithiasis. Which pathophysiologic mechanism best explains these findings?
Answer choices
- AAutonomous secretion of parathyroid hormone by an adenoma
- BMacrophage expression of 1 alpha hydroxylaseCorrect answer
- CInactivating mutation of the calcium sensing receptor
- DIncreased osteoclast activity due to calcitonin deficiency
- ERenal failure causing phosphate retention
- FIncreased intestinal expression of calcium-binding proteins due to vitamin D receptor upregulation
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