Clinical biochemistry: creatinine clearance: 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: creatinine clearance

Sample item

A 24-hour urine collection has a volume of 1440 mL and urine creatinine of 90 mg/dL. Plasma creatinine is 1.5 mg/dL. What is the creatinine clearance?

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

The answer and the reasoning

A. 60 mL/min

Clearance = (urine concentration x urine flow rate) / plasma concentration. The flow rate is 1440 mL per 1440 minutes = 1 mL/min, so clearance = (90 x 1) / 1.5 = 60 mL/min. Creatinine clearance slightly overestimates GFR because a small amount is secreted by the tubule.

Option by option

  • A. 60 mL/min (correct)

    Correct. (90 x 1) / 1.5 = 60 mL/min.

  • B. 120 mL/min

    120 mL/min is not obtained with any correct use of the given values.

  • C. 30 mL/min

    30 mL/min would need a urine creatinine of 45 mg/dL or a plasma creatinine of 3.0 mg/dL, and does not follow from the given values.

  • D. 90 mL/min

    90 mL/min results from omitting division by the plasma creatinine.

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, 60 mL/min. Clearance = (urine concentration x urine flow rate) / plasma concentration.

Why is "120 mL/min" not the answer?

120 mL/min is not obtained with any correct use of the given values.

Why is "30 mL/min" not the answer?

30 mL/min would need a urine creatinine of 45 mg/dL or a plasma creatinine of 3.0 mg/dL, and does not follow from the given values.

Why is "90 mL/min" not the answer?

90 mL/min results from omitting division by the plasma creatinine.

What concept does this question test?

It tests Clinical biochemistry: creatinine clearance in Biochemistry. The flow rate is 1440 mL per 1440 minutes = 1 mL/min, so clearance = (90 x 1) / 1.5 = 60 mL/min. Creatinine clearance slightly overestimates GFR because a small amount is secreted by the tubule.

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: creatinine clearance?

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.