Clinical biochemistry: colorimetry calculation: 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: colorimetry calculation

Sample item

In a colorimetric glucose assay, a 200 mg/dL standard gives an absorbance of 0.40 at the same path length. A patient sample gives an absorbance of 0.25. Assuming the Beer-Lambert law applies, what is the sample glucose?

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

The answer and the reasoning

B. 125 mg/dL

By the Beer-Lambert law absorbance is directly proportional to concentration at a fixed path length. Sample concentration = (absorbance of test / absorbance of standard) x standard concentration = (0.25 / 0.40) x 200 = 0.625 x 200 = 125 mg/dL. The relationship holds only in the linear range, so highly concentrated samples are diluted and re-run.

Option by option

  • A. 80 mg/dL

    80 mg/dL results from multiplying the standard concentration by 0.40 instead of by the absorbance ratio.

  • B. 125 mg/dL (correct)

    Correct. (0.25 / 0.40) x 200 = 125 mg/dL.

  • C. 160 mg/dL

    160 mg/dL would need a sample absorbance of 0.32, and does not follow from the given values.

  • D. 320 mg/dL

    320 mg/dL arises from multiplying by the inverted ratio of 1.6.

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 B, 125 mg/dL. By the Beer-Lambert law absorbance is directly proportional to concentration at a fixed path length.

Why is "80 mg/dL" not the answer?

80 mg/dL results from multiplying the standard concentration by 0.40 instead of by the absorbance ratio.

Why is "160 mg/dL" not the answer?

160 mg/dL would need a sample absorbance of 0.32, and does not follow from the given values.

Why is "320 mg/dL" not the answer?

320 mg/dL arises from multiplying by the inverted ratio of 1.6.

What concept does this question test?

It tests Clinical biochemistry: colorimetry calculation in Biochemistry. Sample concentration = (absorbance of test / absorbance of standard) x standard concentration = (0.25 / 0.40) x 200 = 0.625 x 200 = 125 mg/dL. The relationship holds only in the linear range, so highly concentrated samples are diluted and re-run.

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: colorimetry calculation?

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.