Renal tubular acidosis — viva

Branching structured oral on renal tubular acidosis in children, covering the definition as a normal anion gap metabolic acidosis, the three-type classification by potassium direction and urine pH, the urine anion gap as a surrogate for ammonium, the nephrocalcinosis mechanism in distal RTA, the alkali dose difference between distal and proximal RTA, and the safe correction of chronic acidosis.

branching clinical structured oral4 min readVerification in progress

Prompt

A 7-month-old infant presents with failure to thrive, polyuria, and vomiting. Bloods show a normal anion gap metabolic acidosis with a potassium of 2.6 mmol per litre. The urine pH is 6.8 and a renal ultrasound shows bilateral nephrocalcinosis. You are the paediatric registrar. Talk me through your diagnosis and management.

Opening (must-hit)

"This is a normal anion gap (hyperchloraemic) metabolic acidosis in an infant with failure to thrive. The potassium is low at 2.6 and the urine pH is 6.8, persistently above 5.5 despite acidosis, with nephrocalcinosis on ultrasound. That combination is distal (type 1) renal tubular acidosis. My first step is to confirm the anion gap is normal and exclude a high-gap cause, then treat with cautious alkali and potassium, and investigate for the hereditary form with genetics and a hearing assessment. I would correct the acidosis only partially, to a bicarbonate around 12, because over-rapid correction is dangerous." [1][9]

Paediatrics Fellowship Pro

You have read the opening of this viva. The complete unit — every section and its primary-source references — is part of the Paediatrics Fellowship fellowship atlas.

References6Show ledger

[1]Pelletier J; Gbadegesin R; Staples B Renal Tubular Acidosis. Pediatr Rev, 2017.PMID 29093127
[2]Alexander RT; Bitzan M Renal Tubular Acidosis. Pediatr Clin North Am, 2019.PMID 30454739
[3]Wagner CA; Unwin R; Lopez-Garcia SC; Kleta R The pathophysiology of distal renal tubular acidosis. Nat Rev Nephrol, 2023.PMID 37016093
[6]Finer G; Landau D Clinical Approach to Proximal Renal Tubular Acidosis in Children. Adv Chronic Kidney Dis, 2018.PMID 30139461
[9]Kraut JA; Madias NE Metabolic acidosis: pathophysiology, diagnosis and management. Nat Rev Nephrol, 2010.PMID 20308999
[10]Batlle D; Ba Aqeel SH; Marquez A The Urine Anion Gap in Context. Clin J Am Soc Nephrol, 2018.PMID 29311217