Electrolytes: hypomagnesaemia: practice question

A General Medicine 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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General Medicine · Electrolytes: hypomagnesaemia

Sample item

A 66-year-old woman on a proton pump inhibitor for 8 years and on furosemide has persistently low potassium (3.0 mmol/L) and low calcium (corrected 1.95 mmol/L) despite oral supplements. She is asymptomatic with a normal ECG apart from a long QT. Parathyroid hormone is inappropriately low. What is the best next step?

AMeasure serum magnesium and replace it if lowBIncrease the oral calcium dose aloneCStart teriparatide injectionsDBegin intravenous potassium infusion alone

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

The answer and the reasoning

A. Measure serum magnesium and replace it if low

Magnesium deficiency impairs parathyroid hormone secretion and causes end-organ resistance to it, and it also promotes renal potassium wasting, making both hypocalcaemia and hypokalaemia refractory. Long-term PPIs and loop diuretics are common causes. Replacing magnesium corrects the other abnormalities.

Option by option

A. Measure serum magnesium and replace it if low (correct)
Correct. Replacing magnesium restores PTH action and reduces potassium wasting, correcting both abnormalities.
B. Increase the oral calcium dose alone
More calcium alone does not work while magnesium deficiency blunts PTH.
C. Start teriparatide injections
Teriparatide is a PTH analogue used for osteoporosis or hypoparathyroidism, and it would not treat this cause.
D. Begin intravenous potassium infusion alone
Potassium alone will not hold because magnesium deficiency keeps causing renal potassium loss.

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.

Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is A, Measure serum magnesium and replace it if low. Magnesium deficiency impairs parathyroid hormone secretion and causes end-organ resistance to it, and it also promotes renal potassium wasting, making both hypocalcaemia and hypokalaemia refractory.

Why is "Increase the oral calcium dose alone" not the answer?

More calcium alone does not work while magnesium deficiency blunts PTH.

Why is "Start teriparatide injections" not the answer?

Teriparatide is a PTH analogue used for osteoporosis or hypoparathyroidism, and it would not treat this cause.

Why is "Begin intravenous potassium infusion alone" not the answer?

Potassium alone will not hold because magnesium deficiency keeps causing renal potassium loss.

What concept does this question test?

It tests Electrolytes: hypomagnesaemia in General Medicine. Long-term PPIs and loop diuretics are common causes. Replacing magnesium corrects the other abnormalities.

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 Electrolytes: hypomagnesaemia?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.