Renal tubular acidosis — OSCE

Candidate brief

You are the paediatric registrar. A 7-month-old baby has been admitted with poor growth, vomiting and excessive urination. The team has confirmed a genetic kidney condition called hereditary distal renal tubular acidosis: the kidney tubule cannot get rid of acid properly, so the blood becomes too acidic, and calcium deposits (nephrocalcinosis) have formed in the kidney. The baby will need lifelong medicine (alkali/citrate) to neutralise the acid, and a hearing test and genetic testing have been arranged. The parents want to understand what it is, why the baby needs medicine forever, what the calcium deposits and the hearing test mean, and what to watch for. Explain clearly, check understanding, and agree a plan. [1][4]

Marking domains

Clinical knowledge and accuracy (3). Explains that hereditary distal renal tubular acidosis is an inherited defect of the kidney's collecting duct that cannot remove acid, causing a normal-anion-gap acidosis, low potassium, and kidney calcium deposits (nephrocalcinosis) from the acid leaching bone mineral and lowering urinary citrate. Explains that lifelong alkali (citrate) neutralises the acid, restores growth, and reduces the risk of further kidney damage and stones; and that the hearing test is needed because the same gene affects the inner ear. [3][8]

Communication and plain language (3). Avoids jargon or defines it; uses an analogy (the kidney tubule is a "drain that cannot flush out the acid"); paces the information; pauses to check understanding; invites questions. Conveys that it is genetic, usually inherited from both parents, and does not imply anything was done wrong in the pregnancy or care. [1][4]

Management plan and safety-net (3). Explains the lifelong citrate medicine given in divided doses through the day, the need for regular blood tests and kidney ultrasound surveillance, growth monitoring, and the transition to adult kidney care. Gives a clear safety-net: never stop the medicine even when the baby seems well; seek help for vomiting or diarrhoea that prevents the medicine being kept down, severe weakness, or poor feeding; flag the condition and the medicine to any new doctor. [4][8]

Empathy and partnership (1). Acknowledges the worry of a genetic diagnosis in a baby, validates the parents' concern about the poor growth, and frames the diagnosis positively — a named, treatable condition where medicine protects growth and the kidney. [1]

Examiner notes

Strong candidates explain WHY the alkali is lifelong (the tubule defect is permanent, so stopping the medicine lets the acidosis and kidney damage return), name the link between the gene and hearing plainly, and give a concrete safety-net around sick days and medicine adherence rather than vague reassurance. Weak candidates call it "a kidney problem" without explaining the acid defect, minimise the need for lifelong medicine, or omit the hearing test. [3][8]