Clinical biochemistry: hypercalcaemia: 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: hypercalcaemia

Sample item

A 62-year-old smoker with a squamous cell lung carcinoma has confusion, polyuria and serum calcium 13.4 mg/dL. Serum intact parathyroid hormone is suppressed and phosphate is low. Which mediator is the most likely cause?

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

The answer and the reasoning

A. Parathyroid hormone-related peptide

Humoral hypercalcaemia of malignancy is typically due to parathyroid hormone-related peptide, which binds the PTH receptor to increase bone resorption and renal calcium reabsorption and reduce phosphate reabsorption. Normal parathyroids are suppressed by the high calcium, so intact PTH is low, unlike primary hyperparathyroidism. Squamous carcinomas are classically associated.

Option by option

  • A. Parathyroid hormone-related peptide (correct)

    Correct. PTHrP mimics PTH, raising calcium and suppressing the parathyroid glands.

  • B. Calcitonin from a medullary tumour

    Calcitonin lowers calcium and does not cause hypercalcaemia.

  • C. 1,25-dihydroxyvitamin D from a granuloma

    Granuloma-derived calcitriol is seen in sarcoidosis with low PTH but phosphate is usually normal or high.

  • D. Parathyroid hormone from an adenoma

    A parathyroid adenoma would give high or inappropriately normal PTH.

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 A, Parathyroid hormone-related peptide. Humoral hypercalcaemia of malignancy is typically due to parathyroid hormone-related peptide, which binds the PTH receptor to increase bone resorption and renal calcium reabsorption and reduce phosphate reabsorption.

Why is "Calcitonin from a medullary tumour" not the answer?

Calcitonin lowers calcium and does not cause hypercalcaemia.

Why is "1,25-dihydroxyvitamin D from a granuloma" not the answer?

Granuloma-derived calcitriol is seen in sarcoidosis with low PTH but phosphate is usually normal or high.

Why is "Parathyroid hormone from an adenoma" not the answer?

A parathyroid adenoma would give high or inappropriately normal PTH.

What concept does this question test?

It tests Clinical biochemistry: hypercalcaemia in Biochemistry. Normal parathyroids are suppressed by the high calcium, so intact PTH is low, unlike primary hyperparathyroidism. Squamous carcinomas are classically associated.

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: hypercalcaemia?

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.