Clinical biochemistry: delta ratio in mixed acid-base disorders: 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: delta ratio in mixed acid-base disorders

Sample item

A man with diabetic ketoacidosis has also vomited repeatedly. Na is 140, Cl 90 and HCO3 18 mmol/L. Taking a normal anion gap as 12 and normal bicarbonate as 24, what is the delta ratio and its interpretation?

AAbout 3.3, indicating an additional metabolic alkalosisBAbout 1.2, indicating a pure high anion gap acidosisCAbout 0.6, indicating a pure respiratory acidosisDAbout 0.3, indicating an additional normal anion gap acidosis

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

The answer and the reasoning

A. About 3.3, indicating an additional metabolic alkalosis

The anion gap is 140 minus 90 minus 18, or 32, so the rise above normal is 20. Bicarbonate has fallen by 6. The ratio of 20 to 6 is about 3.3. A ratio above 2 means bicarbonate fell less than the gap rose, suggesting an additional metabolic alkalosis, here from vomiting.

Option by option

A. About 3.3, indicating an additional metabolic alkalosis (correct)
Correct. A delta ratio above 2 indicates coexisting metabolic alkalosis.
B. About 1.2, indicating a pure high anion gap acidosis
A ratio of 1 to 2 indicates a pure high anion gap acidosis, which does not fit the numbers.
C. About 0.6, indicating a pure respiratory acidosis
The delta ratio is calculated from metabolic variables and cannot identify a respiratory acidosis.
D. About 0.3, indicating an additional normal anion gap acidosis
A ratio below 1 would suggest a coexisting normal anion gap acidosis, but the ratio here is above 2.

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, About 3.3, indicating an additional metabolic alkalosis. The anion gap is 140 minus 90 minus 18, or 32, so the rise above normal is 20.

Why is "About 1.2, indicating a pure high anion gap acidosis" not the answer?

A ratio of 1 to 2 indicates a pure high anion gap acidosis, which does not fit the numbers.

Why is "About 0.6, indicating a pure respiratory acidosis" not the answer?

The delta ratio is calculated from metabolic variables and cannot identify a respiratory acidosis.

Why is "About 0.3, indicating an additional normal anion gap acidosis" not the answer?

A ratio below 1 would suggest a coexisting normal anion gap acidosis, but the ratio here is above 2.

What concept does this question test?

It tests Clinical biochemistry: delta ratio in mixed acid-base disorders in Biochemistry. Bicarbonate has fallen by 6. The ratio of 20 to 6 is about 3.3. A ratio above 2 means bicarbonate fell less than the gap rose, suggesting an additional metabolic alkalosis, here from vomiting.

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: delta ratio in mixed acid-base disorders?

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.