Clinical biochemistry: distal 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: distal renal tubular acidosis

Sample item

A 25-year-old woman with Sjogren syndrome has a normal anion gap metabolic acidosis, hypokalaemia, nephrocalcinosis and a urine pH persistently above 5.5. What is the diagnosis?

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

The answer and the reasoning

D. Distal (type 1) renal tubular acidosis

In distal RTA the collecting duct cannot secrete hydrogen ions, so urine pH stays above 5.5 despite systemic acidosis. Potassium wasting, hypercalciuria with hypocitraturia, stones and nephrocalcinosis are typical, and autoimmune diseases such as Sjogren syndrome are associated. Type 4 causes hyperkalaemia.

Option by option

  • A. Hyporeninaemic hypoaldosteronism (type 4) renal tubular acidosis

    Type 4 RTA causes hyperkalaemia, not hypokalaemia.

  • B. Diarrhoea-related bicarbonate loss

    Diarrhoea causes acidosis with an acidic urine and a positive urine ammonium response.

  • C. Proximal (type 2) renal tubular acidosis

    Proximal RTA is characterised by bicarbonate wasting and a urine pH that falls below 5.5 once serum bicarbonate is low.

  • D. Distal (type 1) renal tubular acidosis (correct)

    Correct. High urine pH with acidosis, hypokalaemia and nephrocalcinosis is distal RTA.

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, Distal (type 1) renal tubular acidosis. In distal RTA the collecting duct cannot secrete hydrogen ions, so urine pH stays above 5.

Why is "Hyporeninaemic hypoaldosteronism (type 4) renal tubular acidosis" not the answer?

Type 4 RTA causes hyperkalaemia, not hypokalaemia.

Why is "Diarrhoea-related bicarbonate loss" not the answer?

Diarrhoea causes acidosis with an acidic urine and a positive urine ammonium response.

Why is "Proximal (type 2) renal tubular acidosis" not the answer?

Proximal RTA is characterised by bicarbonate wasting and a urine pH that falls below 5.5 once serum bicarbonate is low.

What concept does this question test?

It tests Clinical biochemistry: distal renal tubular acidosis in Biochemistry. 5 despite systemic acidosis. Potassium wasting, hypercalciuria with hypocitraturia, stones and nephrocalcinosis are typical, and autoimmune diseases such as Sjogren syndrome are associated. Type 4 causes hyperkalaemia.

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 Clinical biochemistry: distal 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.