Endocrinology: SIADH: 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 · Endocrinology: SIADH

Sample item

A euvolemic patient with small-cell lung cancer has serum sodium 118 mmol/L, low serum osmolality, and inappropriately concentrated urine. Which mechanism best explains the hyponatremia?

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

The answer and the reasoning

C. Excess antidiuretic hormone activity

SIADH causes water retention through inappropriate antidiuretic hormone activity, producing hypotonic hyponatremia with inappropriately concentrated urine in an apparently euvolemic patient. Small-cell lung cancer is a recognized cause.

Option by option

  • A. Diabetes insipidus

    Diabetes insipidus causes inability to concentrate urine and often hypernatremia.

  • B. Osmotic diuresis from glucosuria

    Glucosuria causes water loss, not this concentrated-urine euvolemic hyponatremia pattern.

  • C. Excess antidiuretic hormone activity (correct)

    Correct. ADH-mediated water retention produces this biochemical pattern.

  • D. Aldosterone excess

    Aldosterone excess tends to retain sodium and promote 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.

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Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Excess antidiuretic hormone activity. SIADH causes water retention through inappropriate antidiuretic hormone activity, producing hypotonic hyponatremia with inappropriately concentrated urine in an apparently euvolemic patient.

Why is "Diabetes insipidus" not the answer?

Diabetes insipidus causes inability to concentrate urine and often hypernatremia.

Why is "Osmotic diuresis from glucosuria" not the answer?

Glucosuria causes water loss, not this concentrated-urine euvolemic hyponatremia pattern.

Why is "Aldosterone excess" not the answer?

Aldosterone excess tends to retain sodium and promote potassium loss.

What concept does this question test?

It tests Endocrinology: SIADH in General Medicine. Small-cell lung cancer is a recognized cause.

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 Endocrinology: SIADH?

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.