Electrolyte Disorders USMLE Step 1 Practice Question
A 65-year-old man with metastatic colon cancer presents with severe weakness, constipation, and polyuria. Vital signs: BP 92/58, HR 108, RR 18, Temp 37.2°C, SpO2 98% on room air. Serum calcium is 15.1 mg/dL; PTH is suppressed. Urinalysis shows no proteinuria. He denies recent thiazide use. Large-volume isotonic saline infusion is initiated. Which of the following best explains why this initial therapy helps lower his serum calcium level?
Answer choices
- AIt directly inhibits osteoclast activity
- BIt promotes intracellular shift of calcium
- CIt increases glomerular filtration and urinary calcium excretionCorrect answer
- DIt binds serum calcium in the bloodstream
- EIt increases intestinal calcium absorption
- FF. It enhances calcitonin secretion and inhibits PTH-related peptide production
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