Clinical biochemistry: corrected sodium in hyperglycaemia: 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: corrected sodium in hyperglycaemia

Sample item

A 65-year-old man with type 2 diabetes is drowsy and dehydrated. Serum sodium is 126 mmol/L and plasma glucose 600 mg/dL. Using the correction of 1.6 mmol/L of sodium for each 100 mg/dL rise in glucose above 100 mg/dL, what is the best interpretation?

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

The answer and the reasoning

D. Corrected sodium about 134 mmol/L, so the hyponatraemia is largely translocational

Hyperglycaemia draws water from cells into the extracellular fluid, diluting sodium. Corrected sodium = 126 + 1.6 x (600 - 100) / 100 = 126 + 8 = 134 mmol/L. The patient therefore has only mild hyponatraemia, while the plasma is hyperosmolar; treatment is with fluids and insulin, and sodium rises as glucose falls.

Option by option

  • A. Sodium of 126 mmol/L is accurate, so hypertonic saline is required

    Hypertonic saline in a hyperosmolar state would be harmful and the true value is higher.

  • B. Corrected sodium about 142 mmol/L, so no electrolyte abnormality exists

    The correction adds only 8 mmol/L, giving 134 and not 142, and the sodium is still low.

  • C. Corrected sodium about 118 mmol/L, so true hyponatraemia is worse

    Subtracting the correction is the wrong direction; high glucose lowers measured sodium.

  • D. Corrected sodium about 134 mmol/L, so the hyponatraemia is largely translocational (correct)

    Correct. 126 + 8 = 134 mmol/L, showing the low sodium is mostly dilutional from glucose.

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 D, Corrected sodium about 134 mmol/L, so the hyponatraemia is largely translocational. Hyperglycaemia draws water from cells into the extracellular fluid, diluting sodium.

Why is "Sodium of 126 mmol/L is accurate, so hypertonic saline is required" not the answer?

Hypertonic saline in a hyperosmolar state would be harmful and the true value is higher.

Why is "Corrected sodium about 142 mmol/L, so no electrolyte abnormality exis…" not the answer?

The correction adds only 8 mmol/L, giving 134 and not 142, and the sodium is still low.

Why is "Corrected sodium about 118 mmol/L, so true hyponatraemia is worse" not the answer?

Subtracting the correction is the wrong direction; high glucose lowers measured sodium.

What concept does this question test?

It tests Clinical biochemistry: corrected sodium in hyperglycaemia in Biochemistry. Corrected sodium = 126 + 1.6 x (600 - 100) / 100 = 126 + 8 = 134 mmol/L. The patient therefore has only mild hyponatraemia, while the plasma is hyperosmolar; treatment is with fluids and insulin, and sodium rises as glucose falls.

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 sodium in hyperglycaemia?

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.