Clinical biochemistry: hypoparathyroidism after thyroidectomy: 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 · Clinical biochemistry: hypoparathyroidism after thyroidectomy

Sample item

Two days after total thyroidectomy, a woman has perioral tingling, and inflating a blood pressure cuff above systolic pressure induces carpopedal spasm. Which laboratory pattern is expected?

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

The answer and the reasoning

C. Low calcium, high phosphate, low PTH

Accidental removal or devascularisation of the parathyroids causes hypoparathyroidism. Low PTH reduces bone resorption and renal calcium reabsorption, and phosphate excretion falls, giving hypocalcaemia with hyperphosphataemia. The carpopedal spasm described is Trousseau sign.

Option by option

  • A. Low calcium, low phosphate, high PTH

    Low calcium with low phosphate and high PTH fits vitamin D deficiency.

  • B. Low calcium, high phosphate, high PTH

    Low calcium, high phosphate and high PTH fits chronic kidney disease or PTH resistance.

  • C. Low calcium, high phosphate, low PTH (correct)

    Correct. Low PTH gives low calcium and high phosphate.

  • D. High calcium, low phosphate, high PTH

    High calcium with low phosphate and high PTH fits primary hyperparathyroidism.

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, Low calcium, high phosphate, low PTH. Accidental removal or devascularisation of the parathyroids causes hypoparathyroidism.

Why is "Low calcium, low phosphate, high PTH" not the answer?

Low calcium with low phosphate and high PTH fits vitamin D deficiency.

Why is "Low calcium, high phosphate, high PTH" not the answer?

Low calcium, high phosphate and high PTH fits chronic kidney disease or PTH resistance.

Why is "High calcium, low phosphate, high PTH" not the answer?

High calcium with low phosphate and high PTH fits primary hyperparathyroidism.

What concept does this question test?

It tests Clinical biochemistry: hypoparathyroidism after thyroidectomy in Biochemistry. Low PTH reduces bone resorption and renal calcium reabsorption, and phosphate excretion falls, giving hypocalcaemia with hyperphosphataemia. The carpopedal spasm described is Trousseau sign.

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 Clinical biochemistry: hypoparathyroidism after thyroidectomy?

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.