Clinical biochemistry: biotin interference: practice question

A Biochemistry 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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Biochemistry · Clinical biochemistry: biotin interference

Sample item

A woman taking high-dose biotin supplements for hair loss has a thyroid profile showing very low TSH with high free T4 and free T3, though she has no symptoms of thyrotoxicosis. Which explanation fits best?

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

The answer and the reasoning

C. Interference with streptavidin-biotin immunoassays, lowering sandwich results and raising competitive results

Many immunoassays use biotinylated antibodies captured on streptavidin. Excess biotin competes for the streptavidin sites, which falsely lowers results in sandwich assays such as TSH and falsely raises results in competitive assays such as free T4. Stopping biotin before blood sampling resolves the interference.

Option by option

  • A. Pituitary resistance to thyroid hormone

    Pituitary resistance to thyroid hormone causes raised TSH with raised thyroid hormones, not low TSH.

  • B. Autoimmune thyroiditis with hormone leak

    Thyroiditis with hormone leak would give symptoms of thyrotoxicosis, which she lacks.

  • C. Interference with streptavidin-biotin immunoassays, lowering sandwich results and raising competitive results (correct)

    Correct. Excess biotin interferes with the streptavidin capture step, lowering sandwich and raising competitive results.

  • D. True thyrotoxicosis from biotin stimulating the thyroid

    Biotin is a vitamin and does not stimulate the thyroid 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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Interference with streptavidin-biotin immunoassays, lowering sandwich results and raising competitive results. Many immunoassays use biotinylated antibodies captured on streptavidin.

Why is "Pituitary resistance to thyroid hormone" not the answer?

Pituitary resistance to thyroid hormone causes raised TSH with raised thyroid hormones, not low TSH.

Why is "Autoimmune thyroiditis with hormone leak" not the answer?

Thyroiditis with hormone leak would give symptoms of thyrotoxicosis, which she lacks.

Why is "True thyrotoxicosis from biotin stimulating the thyroid" not the answer?

Biotin is a vitamin and does not stimulate the thyroid gland.

What concept does this question test?

It tests Clinical biochemistry: biotin interference in Biochemistry. Excess biotin competes for the streptavidin sites, which falsely lowers results in sandwich assays such as TSH and falsely raises results in competitive assays such as free T4. Stopping biotin before blood sampling resolves the interference.

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 Clinical biochemistry: biotin interference?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.