Minerals: corrected calcium: 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 · Minerals: corrected calcium

Sample item

A 30-year-old woman with nephrotic syndrome has no tetany. Serum total calcium is 7.2 mg/dL and albumin is 2.0 g/dL. Using the correction of 0.8 mg/dL of calcium for every 1 g/dL that albumin is below 4.0, what is the interpretation?

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

The answer and the reasoning

C. Corrected calcium is about 8.8 mg/dL, which is normal, so no calcium replacement is needed

Corrected calcium equals measured calcium plus 0.8 x (4.0 minus albumin). Here it is 7.2 + 0.8 x 2.0 = 7.2 + 1.6 = 8.8 mg/dL. Low total calcium from hypoalbuminaemia reflects reduced protein-bound calcium, while the ionised fraction is normal. Ionised calcium can be measured if there is doubt.

Option by option

  • A. Corrected calcium is about 5.6 mg/dL, which needs intravenous calcium gluconate

    5.6 results from subtracting the correction (7.2 minus 1.6) instead of adding it.

  • B. Corrected calcium is 7.2 mg/dL, which needs oral calcium

    Ignoring albumin treats the low protein-bound fraction as true hypocalcaemia.

  • C. Corrected calcium is about 8.8 mg/dL, which is normal, so no calcium replacement is needed (correct)

    7.2 plus 1.6 gives 8.8, which is within the normal range, so the ionised calcium is normal.

  • D. Corrected calcium is about 10.4 mg/dL, which indicates hypercalcaemia

    10.4 results from doubling the correction to 3.2, which is arithmetically wrong.

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, Corrected calcium is about 8.8 mg/dL, which is normal, so no calcium replacement is needed. Corrected calcium equals measured calcium plus 0.

Why is "Corrected calcium is about 5.6 mg/dL, which needs intravenous calcium…" not the answer?

5.6 results from subtracting the correction (7.2 minus 1.6) instead of adding it.

Why is "Corrected calcium is 7.2 mg/dL, which needs oral calcium" not the answer?

Ignoring albumin treats the low protein-bound fraction as true hypocalcaemia.

Why is "Corrected calcium is about 10.4 mg/dL, which indicates hypercalcaemia" not the answer?

10.4 results from doubling the correction to 3.2, which is arithmetically wrong.

What concept does this question test?

It tests Minerals: corrected calcium in Biochemistry. 8 x (4.0 minus albumin). Here it is 7.2 + 0.8 x 2.0 = 7.2 + 1.6 = 8.8 mg/dL. Low total calcium from hypoalbuminaemia reflects reduced protein-bound calcium, while the ionised fraction is normal. Ionised calcium can be measured if there is doubt.

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 Minerals: corrected calcium?

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.