Urinary proteins: Bence Jones protein: 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 · Urinary proteins: Bence Jones protein

Sample item

A 62-year-old man with back pain and anaemia has a negative urine dipstick for protein, but sulfosalicylic acid gives a heavy precipitate. On heating, turbidity appears at about 56 degrees Celsius, clears on boiling and returns on cooling. What explains the negative dipstick?

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

The answer and the reasoning

A. The dipstick detects mainly albumin and is insensitive to free light chains

Bence Jones protein consists of free monoclonal light chains that precipitate at 40 to 60 degrees Celsius and redissolve near boiling. Reagent strips use a pH indicator that responds mostly to albumin, so they miss light chains, while acid precipitation tests detect them. Urine electrophoresis with immunofixation confirms the diagnosis.

Option by option

  • A. The dipstick detects mainly albumin and is insensitive to free light chains (correct)

    Correct. Strips are albumin-specific and miss light chains.

  • B. The urine is too alkaline for light chains to precipitate

    Alkaline urine would not explain a heavy positive acid precipitation test.

  • C. Light chains are too large to reach the dipstick

    Light chains are small and filtered freely, which is why they appear in urine.

  • D. There is no protein in the urine and the precipitate is artefact

    A precipitate with a heat pattern indicates real protein and not artefact.

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 A, The dipstick detects mainly albumin and is insensitive to free light chains. Bence Jones protein consists of free monoclonal light chains that precipitate at 40 to 60 degrees Celsius and redissolve near boiling.

Why is "The urine is too alkaline for light chains to precipitate" not the answer?

Alkaline urine would not explain a heavy positive acid precipitation test.

Why is "Light chains are too large to reach the dipstick" not the answer?

Light chains are small and filtered freely, which is why they appear in urine.

Why is "There is no protein in the urine and the precipitate is artefact" not the answer?

A precipitate with a heat pattern indicates real protein and not artefact.

What concept does this question test?

It tests Urinary proteins: Bence Jones protein in Biochemistry. Reagent strips use a pH indicator that responds mostly to albumin, so they miss light chains, while acid precipitation tests detect them. Urine electrophoresis with immunofixation confirms the diagnosis.

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 Urinary proteins: Bence Jones protein?

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.