Clinical biochemistry: 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.

Try it

Biochemistry · Clinical biochemistry: corrected calcium

Sample item

A malnourished patient with nephrotic syndrome has a total serum calcium of 7.2 mg/dL and albumin of 2.0 g/dL. Using the standard correction, what is the albumin-corrected calcium and what does it mean?

A8.8 mg/dL, which is within the normal rangeB7.2 mg/dL, which is unchanged by albuminC9.6 mg/dL, which is hypercalcaemiaD6.4 mg/dL, which is severe hypocalcaemia

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

The answer and the reasoning

A. 8.8 mg/dL, which is within the normal range

Corrected calcium = measured calcium + 0.8 x (4.0 - albumin) = 7.2 + 0.8 x 2.0 = 8.8 mg/dL. About 40% of calcium is protein-bound, so low albumin lowers total calcium without changing the physiologically active ionised fraction. Ionised calcium measurement is the best test when in doubt.

Option by option

A. 8.8 mg/dL, which is within the normal range (correct)
Correct. After correction the value of 8.8 mg/dL is normal, a pseudohypocalcaemia.
B. 7.2 mg/dL, which is unchanged by albumin
Albumin binding does alter total calcium, so no correction would be wrong here.
C. 9.6 mg/dL, which is hypercalcaemia
9.6 mg/dL is not the result of the formula, and the patient is not hypercalcaemic.
D. 6.4 mg/dL, which is severe hypocalcaemia
Subtracting the correction instead of adding it is the error behind 6.4 mg/dL.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, 8.8 mg/dL, which is within the normal range. Corrected calcium = measured calcium + 0.

Why is "7.2 mg/dL, which is unchanged by albumin" not the answer?

Albumin binding does alter total calcium, so no correction would be wrong here.

Why is "9.6 mg/dL, which is hypercalcaemia" not the answer?

9.6 mg/dL is not the result of the formula, and the patient is not hypercalcaemic.

Why is "6.4 mg/dL, which is severe hypocalcaemia" not the answer?

Subtracting the correction instead of adding it is the error behind 6.4 mg/dL.

What concept does this question test?

It tests Clinical biochemistry: corrected calcium in Biochemistry. 8 x (4.0 - albumin) = 7.2 + 0.8 x 2.0 = 8.8 mg/dL. About 40% of calcium is protein-bound, so low albumin lowers total calcium without changing the physiologically active ionised fraction. Ionised calcium measurement is the best test when in 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 Clinical biochemistry: 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.