Nephrology and electrolytes: Bartter syndrome site of defect: 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 · Nephrology and electrolytes: Bartter syndrome site of defect

Sample item

A 4-year-old child has failure to thrive, polyuria and muscle weakness. Investigations show potassium 2.6 mmol/L, metabolic alkalosis, raised renin and aldosterone, normal blood pressure and high urinary calcium excretion. There is no diuretic exposure. Which nephron segment is primarily affected?

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

The answer and the reasoning

C. Thick ascending limb of the loop of Henle

Bartter syndrome results from defective salt reabsorption in the thick ascending limb, mimicking chronic loop diuretic use. The picture is hypokalaemic alkalosis with normal or low blood pressure, hyperreninaemic hyperaldosteronism and hypercalciuria. Gitelman syndrome, in the distal tubule, has low urinary calcium.

Option by option

  • A. Proximal convoluted tubule

    Proximal tubule dysfunction causes bicarbonate, phosphate, glucose and amino acid wasting.

  • B. Cortical collecting duct principal cells

    Collecting duct sodium channel overactivity causes hypertension with low renin and hypokalaemia.

  • C. Thick ascending limb of the loop of Henle (correct)

    Correct. A loop-diuretic-like defect gives hypokalaemic alkalosis with hypercalciuria.

  • D. Distal convoluted tubule

    Distal tubule defects mimic thiazides and cause hypocalciuria and hypomagnesaemia.

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, Thick ascending limb of the loop of Henle. Bartter syndrome results from defective salt reabsorption in the thick ascending limb, mimicking chronic loop diuretic use.

Why is "Proximal convoluted tubule" not the answer?

Proximal tubule dysfunction causes bicarbonate, phosphate, glucose and amino acid wasting.

Why is "Cortical collecting duct principal cells" not the answer?

Collecting duct sodium channel overactivity causes hypertension with low renin and hypokalaemia.

Why is "Distal convoluted tubule" not the answer?

Distal tubule defects mimic thiazides and cause hypocalciuria and hypomagnesaemia.

What concept does this question test?

It tests Nephrology and electrolytes: Bartter syndrome site of defect in General Medicine. The picture is hypokalaemic alkalosis with normal or low blood pressure, hyperreninaemic hyperaldosteronism and hypercalciuria. Gitelman syndrome, in the distal tubule, has low urinary calcium.

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 Nephrology and electrolytes: Bartter syndrome site of defect?

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.