Nephrology: acute kidney injury: 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: acute kidney injury

Sample item

A man develops acute kidney injury after 3 days of vomiting and diarrhoea. Which set of findings best supports a pre-renal cause rather than acute tubular necrosis?

AFractional excretion of sodium below 1%, urine osmolality above 500 mOsm/kg and bland sedimentBWhite cell casts with eosinophilsCRed cell casts with dysmorphic red cellsDFractional excretion of sodium above 2%, urine osmolality about 300 mOsm/kg and muddy brown granular casts

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

The answer and the reasoning

A. Fractional excretion of sodium below 1%, urine osmolality above 500 mOsm/kg and bland sediment

In pre-renal azotaemia, the kidney avidly conserves sodium and water, so urine sodium and fractional sodium excretion are low and the urine is concentrated, with a benign sediment. In acute tubular necrosis, tubular concentrating ability is lost, so FeNa is above 2% and osmolality is near that of plasma, with muddy brown casts.

Option by option

A. Fractional excretion of sodium below 1%, urine osmolality above 500 mOsm/kg and bland sediment (correct)
Correct. Preserved tubular function gives a low FeNa, concentrated urine and a bland sediment.
B. White cell casts with eosinophils
White cell casts with eosinophils suggest acute interstitial nephritis.
C. Red cell casts with dysmorphic red cells
Dysmorphic red cells and red cell casts indicate glomerulonephritis.
D. Fractional excretion of sodium above 2%, urine osmolality about 300 mOsm/kg and muddy brown granular casts
These are the findings of established acute tubular necrosis.

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, Fractional excretion of sodium below 1%, urine osmolality above 500 mOsm/kg and bland sediment. In pre-renal azotaemia, the kidney avidly conserves sodium and water, so urine sodium and fractional sodium excretion are low and the urine is concentrated, with a benign sediment.

Why is "White cell casts with eosinophils" not the answer?

White cell casts with eosinophils suggest acute interstitial nephritis.

Why is "Red cell casts with dysmorphic red cells" not the answer?

Dysmorphic red cells and red cell casts indicate glomerulonephritis.

Why is "Fractional excretion of sodium above 2%, urine osmolality about 300 m…" not the answer?

These are the findings of established acute tubular necrosis.

What concept does this question test?

It tests Nephrology: acute kidney injury in General Medicine. In acute tubular necrosis, tubular concentrating ability is lost, so FeNa is above 2% and osmolality is near that of plasma, with muddy brown casts.

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 Nephrology: acute kidney injury?

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.