Nuclear medicine: effect of iodinated contrast on radioiodine uptake: 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 · Nuclear medicine: effect of iodinated contrast on radioiodine uptake

Sample item

A woman with suspected Graves disease had a contrast-enhanced CT three weeks ago. A radioiodine uptake test now shows unexpectedly low uptake. What is the likeliest explanation?

AGraves disease is excluded by the low uptakeBTechnetium interfered with the studyCThe iodine load from contrast has saturated the thyroid and reduced radioiodine uptake for several weeksDThe thyroid has been destroyed by the contrast

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

The answer and the reasoning

C. The iodine load from contrast has saturated the thyroid and reduced radioiodine uptake for several weeks

Iodinated contrast contains a large amount of free iodine, which dilutes the administered radioiodine and suppresses uptake for 4 to 8 weeks. Radioiodine studies and therapy should therefore be delayed after contrast. A pertechnetate scan is less affected by this.

Option by option

A. Graves disease is excluded by the low uptake
A low result here is unreliable and does not exclude Graves disease.
B. Technetium interfered with the study
No technetium was given in this scenario.
C. The iodine load from contrast has saturated the thyroid and reduced radioiodine uptake for several weeks (correct)
Correct. Stable iodine competes with radioiodine for uptake.
D. The thyroid has been destroyed by the contrast
Contrast does not destroy the gland.

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, The iodine load from contrast has saturated the thyroid and reduced radioiodine uptake for several weeks. Iodinated contrast contains a large amount of free iodine, which dilutes the administered radioiodine and suppresses uptake for 4 to 8 weeks.

Why is "Graves disease is excluded by the low uptake" not the answer?

A low result here is unreliable and does not exclude Graves disease.

Why is "Technetium interfered with the study" not the answer?

No technetium was given in this scenario.

Why is "The thyroid has been destroyed by the contrast" not the answer?

Contrast does not destroy the gland.

What concept does this question test?

It tests Nuclear medicine: effect of iodinated contrast on radioiodine uptake in Radiology. Radioiodine studies and therapy should therefore be delayed after contrast. A pertechnetate scan is less affected by this.

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 Nuclear medicine: effect of iodinated contrast on radioiodine uptake?

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.