Vitamins and minerals: magnesium: 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 · Vitamins and minerals: magnesium

Sample item

A patient on a long-term proton pump inhibitor has tetany. Serum calcium is low and does not rise with calcium infusion alone. Serum magnesium is very low. Why is the calcium low?

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

The answer and the reasoning

C. Hypomagnesaemia impairs PTH secretion and action

Severe hypomagnesaemia impairs PTH release and causes end-organ resistance to PTH, producing hypocalcaemia that resists calcium alone. Magnesium repletion is needed. Prolonged PPI therapy can reduce gut magnesium absorption.

Option by option

  • A. Low magnesium raises PTH excessively

    PTH is low or inappropriately normal in severe hypomagnesaemia.

  • B. Magnesium deficiency raises vitamin D activation

    Magnesium deficiency lowers rather than raises vitamin D activation.

  • C. Hypomagnesaemia impairs PTH secretion and action (correct)

    Correct. Low magnesium causes a functional hypoparathyroid state.

  • D. Magnesium is needed for calcium absorption by calcium-sensing receptor

    The calcium-sensing receptor mediates calcium sensing, not calcium absorption.

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 C, Hypomagnesaemia impairs PTH secretion and action. Severe hypomagnesaemia impairs PTH release and causes end-organ resistance to PTH, producing hypocalcaemia that resists calcium alone.

Why is "Low magnesium raises PTH excessively" not the answer?

PTH is low or inappropriately normal in severe hypomagnesaemia.

Why is "Magnesium deficiency raises vitamin D activation" not the answer?

Magnesium deficiency lowers rather than raises vitamin D activation.

Why is "Magnesium is needed for calcium absorption by calcium-sensing receptor" not the answer?

The calcium-sensing receptor mediates calcium sensing, not calcium absorption.

What concept does this question test?

It tests Vitamins and minerals: magnesium in Biochemistry. Magnesium repletion is needed. Prolonged PPI therapy can reduce gut magnesium absorption.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Vitamins and minerals: magnesium?

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.