Minerals: magnesium and calcium: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Minerals: magnesium and calcium

Sample item

A 55-year-old man with chronic alcohol use and long-term proton pump inhibitor therapy has persistent hypocalcaemia (serum calcium 6.8 mg/dL) and hypokalaemia despite calcium and vitamin D supplements. Serum PTH is inappropriately low-normal. What is the best next step?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Measure serum magnesium and replace it if low

Magnesium depletion impairs PTH secretion and causes end-organ resistance to PTH, so hypocalcaemia is refractory until magnesium is corrected. Alcohol use, diarrhoea and prolonged PPI therapy are common causes, and hypokalaemia often coexists because of renal potassium wasting.

Option by option

  • A. Arrange parathyroid imaging

    Parathyroid imaging looks for hyperparathyroidism, whereas this is a state of low PTH action.

  • B. Start a thiazide diuretic

    Thiazides reduce urinary calcium excretion but do not treat the cause and can worsen potassium and magnesium loss.

  • C. Increase the dose of calcitriol further

    More calcitriol does not fix the underlying magnesium-related PTH failure and risks hypercalciuria.

  • D. Measure serum magnesium and replace it if low (correct)

    Correcting magnesium restores PTH release and action, which corrects refractory hypocalcaemia and hypokalaemia.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Measure serum magnesium and replace it if low. Magnesium depletion impairs PTH secretion and causes end-organ resistance to PTH, so hypocalcaemia is refractory until magnesium is corrected.

Why is "Arrange parathyroid imaging" not the answer?

Parathyroid imaging looks for hyperparathyroidism, whereas this is a state of low PTH action.

Why is "Start a thiazide diuretic" not the answer?

Thiazides reduce urinary calcium excretion but do not treat the cause and can worsen potassium and magnesium loss.

Why is "Increase the dose of calcitriol further" not the answer?

More calcitriol does not fix the underlying magnesium-related PTH failure and risks hypercalciuria.

What concept does this question test?

It tests Minerals: magnesium and calcium in Biochemistry. Alcohol use, diarrhoea and prolonged PPI therapy are common causes, and hypokalaemia often coexists because of renal potassium wasting.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Minerals: magnesium and calcium?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.