Acid-base: hyperkalaemic acidosis in diabetes: practice question

A General Medicine 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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General Medicine · Acid-base: hyperkalaemic acidosis in diabetes

Sample item

A 62-year-old man with long-standing diabetes and an eGFR of 40 has potassium 5.9 mmol/L, bicarbonate 17 mmol/L, sodium 138 mmol/L and chloride 110 mmol/L. Urine pH is 5.0. Which is the most likely explanation?

AType 1 renal tubular acidosis from failure of distal hydrogen secretionBLactic acidosis from metformin accumulationCType 4 renal tubular acidosis from hyporeninaemic hypoaldosteronismDType 2 renal tubular acidosis from proximal bicarbonate wasting

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

The answer and the reasoning

C. Type 4 renal tubular acidosis from hyporeninaemic hypoaldosteronism

Diabetic nephropathy damages the juxtaglomerular apparatus, causing low renin and low aldosterone. Reduced sodium reabsorption and potassium and hydrogen secretion produce hyperkalaemia and a normal anion gap acidosis, with urine that still acidifies (pH below 5.5). The anion gap here is 138 minus 110 minus 17, which is 11.

Option by option

A. Type 1 renal tubular acidosis from failure of distal hydrogen secretion
Distal RTA gives hypokalaemia and urine pH above 5.5.
B. Lactic acidosis from metformin accumulation
Lactic acidosis raises the anion gap, and it is normal here.
C. Type 4 renal tubular acidosis from hyporeninaemic hypoaldosteronism (correct)
Correct. Hyperkalaemia, a normal anion gap, acidifiable urine and diabetic nephropathy fit type 4 RTA.
D. Type 2 renal tubular acidosis from proximal bicarbonate wasting
Proximal RTA is associated with hypokalaemia and often Fanconi features, not hyperkalaemia.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Type 4 renal tubular acidosis from hyporeninaemic hypoaldosteronism. Diabetic nephropathy damages the juxtaglomerular apparatus, causing low renin and low aldosterone.

Why is "Type 1 renal tubular acidosis from failure of distal hydrogen secreti…" not the answer?

Distal RTA gives hypokalaemia and urine pH above 5.5.

Why is "Lactic acidosis from metformin accumulation" not the answer?

Lactic acidosis raises the anion gap, and it is normal here.

Why is "Type 2 renal tubular acidosis from proximal bicarbonate wasting" not the answer?

Proximal RTA is associated with hypokalaemia and often Fanconi features, not hyperkalaemia.

What concept does this question test?

It tests Acid-base: hyperkalaemic acidosis in diabetes in General Medicine. Reduced sodium reabsorption and potassium and hydrogen secretion produce hyperkalaemia and a normal anion gap acidosis, with urine that still acidifies (pH below 5.5). The anion gap here is 138 minus 110 minus 17, which is 11.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Acid-base: hyperkalaemic acidosis in diabetes?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.