Contrast agents: metformin and iodinated contrast: practice question

A Radiology 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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Radiology · Contrast agents: metformin and iodinated contrast

Sample item

A diabetic patient on metformin with an eGFR of 25 mL/min is to receive intravenous iodinated contrast for an urgent CT. What is the best practice?

AContinue metformin unchanged because contrast never affects renal functionBGive oral bicarbonate and continue metforminCWithhold metformin at the time of contrast and for about 48 hours afterwards, restarting once renal function is confirmed stableDDouble the metformin dose to counter the contrast

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

The answer and the reasoning

C. Withhold metformin at the time of contrast and for about 48 hours afterwards, restarting once renal function is confirmed stable

With severe renal impairment, contrast-induced kidney injury could cause metformin accumulation and lactic acidosis. Metformin is therefore held and restarted only after renal function is rechecked. Urgent imaging should not be delayed because of this precaution.

Option by option

A. Continue metformin unchanged because contrast never affects renal function
Contrast can impair renal function, so continuing blindly is unsafe.
B. Give oral bicarbonate and continue metformin
Bicarbonate does not remove the need to hold metformin.
C. Withhold metformin at the time of contrast and for about 48 hours afterwards, restarting once renal function is confirmed stable (correct)
Correct. Hold metformin and recheck renal function before restarting.
D. Double the metformin dose to counter the contrast
Increasing the dose would worsen the risk of lactic acidosis.

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 Radiology question

What is the answer to this Radiology question?

The best answer is C, Withhold metformin at the time of contrast and for about 48 hours afterwards, restarting once renal function is confirmed stable. With severe renal impairment, contrast-induced kidney injury could cause metformin accumulation and lactic acidosis.

Why is "Continue metformin unchanged because contrast never affects renal fun…" not the answer?

Contrast can impair renal function, so continuing blindly is unsafe.

Why is "Give oral bicarbonate and continue metformin" not the answer?

Bicarbonate does not remove the need to hold metformin.

Why is "Double the metformin dose to counter the contrast" not the answer?

Increasing the dose would worsen the risk of lactic acidosis.

What concept does this question test?

It tests Contrast agents: metformin and iodinated contrast in Radiology. Metformin is therefore held and restarted only after renal function is rechecked. Urgent imaging should not be delayed because of this precaution.

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 Contrast agents: metformin and iodinated contrast?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology 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.