Clinical biochemistry: type 4 renal tubular acidosis: 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: type 4 renal tubular acidosis

Sample item

A 62-year-old with long-standing diabetes and mild chronic kidney disease has potassium 5.9 mmol/L, bicarbonate 18 mmol/L, a normal anion gap, urine pH below 5.5, and low renin and aldosterone. What is the diagnosis?

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

The answer and the reasoning

A. Type 4 renal tubular acidosis

Hyporeninaemic hypoaldosteronism, common in diabetic nephropathy, causes hyperkalaemic normal anion gap acidosis with preserved urinary acidification. Low aldosterone reduces potassium and hydrogen ion secretion. Type 1 and type 2 usually cause hypokalaemia.

Option by option

  • A. Type 4 renal tubular acidosis (correct)

    Correct. Hyperkalaemia with low aldosterone and an acidic urine fits type 4.

  • B. Type 1 distal renal tubular acidosis

    Distal acidosis cannot acidify urine below pH 5.5 and causes hypokalaemia.

  • C. Type 2 proximal renal tubular acidosis

    Proximal acidosis causes bicarbonate wasting and hypokalaemia.

  • D. Diabetic ketoacidosis

    Ketoacidosis would have a high anion gap.

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 A, Type 4 renal tubular acidosis. Hyporeninaemic hypoaldosteronism, common in diabetic nephropathy, causes hyperkalaemic normal anion gap acidosis with preserved urinary acidification.

Why is "Type 1 distal renal tubular acidosis" not the answer?

Distal acidosis cannot acidify urine below pH 5.5 and causes hypokalaemia.

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

Proximal acidosis causes bicarbonate wasting and hypokalaemia.

Why is "Diabetic ketoacidosis" not the answer?

Ketoacidosis would have a high anion gap.

What concept does this question test?

It tests Clinical biochemistry: type 4 renal tubular acidosis in Biochemistry. Low aldosterone reduces potassium and hydrogen ion secretion. Type 1 and type 2 usually cause hypokalaemia.

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: type 4 renal tubular acidosis?

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.