A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 68-year-old man with a history of hypertension and GERD, currently on a thiazide diuretic and a proton pump inhibitor, presents with lethargy and muscle weakness. His temperature is 36.8°C (98.2°F), pulse is 76/min, and blood pressure is 138/86 mmHg. Physical examination reveals decreased deep tendon reflexes. Laboratory studies show: serum magnesium 0.9 mEq/L, potassium 3.0 mEq/L, and calcium 7.8 mg/dL. Which of the following best explains the patient's electrolyte abnormalities?
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A
Magnesium deficiency causing renal potassium wastingIncorrect. True downstream effect of magnesium deficiency, but the question asks for the root cause of magnesium loss itself.
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B
Magnesium deficiency impairing parathyroid hormone releaseIncorrect. Magnesium deficiency impairs PTH release (contributing to low calcium), but isn't the underlying cause of the magnesium loss.
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C
Proton pump inhibitor causing intestinal magnesium lossCorrect. PPIs reduce intestinal magnesium absorption, leading to hypomagnesemia and downstream potassium and calcium abnormalities here.
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D
Calcium deficiency due to impaired intestinal absorptionIncorrect. Calcium absorption is impaired secondary to magnesium-related PTH dysfunction, not from a primary intestinal calcium absorption defect.
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E
Thiazide-induced renal magnesium wastingIncorrect. Thiazides can cause some renal magnesium wasting, but PPI-induced intestinal loss is the dominant mechanism in this case.
↑ Tap an answer to reveal the reasoning
Answer: C. The patient's low magnesium is likely due to the proton pump inhibitor causing intestinal magnesium loss. This leads to hypokalemia and hypocalcemia because magnesium deficiency impairs PTH secretion and responsiveness, as well as causing renal potassium wasting through ROMK disinhibition. While thiazides can cause renal magnesium wasting, the PPI is a more direct cause of magnesium deficiency here. Thiazide-induced renal magnesium wasting is less likely because thiazides primarily cause renal potassium loss.