Explain a food allergy diagnostic plan and challenge to an anxious parent — OSCE

Candidate instructions (2 minutes reading time)

You are the paediatric registrar in the allergy clinic. Mrs Chen has brought her 2-year-old daughter, Sophie, for review of a positive peanut allergy test. The GP ordered a food allergy panel because Sophie has moderate eczema. The SPT to peanut was 6 mm; all other foods were negative. Sophie has never eaten peanut. Mrs Chen has read online that a 6 mm wheal means a "severe allergy" and is anxious. [1]

Your task: explain what the SPT result means (sensitisation versus clinical allergy), outline the diagnostic pathway, address safety concerns, and agree on a plan. You have 8 minutes. [3]

Marking domains

Domain 1: Communication and rapport (25%) — Uses open questions to elicit the mother's understanding and concerns. Avoids jargon; explains sensitisation and clinical allergy in plain language. Acknowledges anxiety without dismissing it. Checks understanding periodically. [1]

Domain 2: Clinical accuracy (30%) — Correctly explains that a positive SPT means sensitisation — the child has peanut-specific IgE — but that approximately 50% of sensitised children tolerate the food on challenge. States that a 6 mm wheal is below the 95% PPV threshold of 8 mm for peanut, so the test alone cannot confirm clinical allergy. Outlines the pathway: component-resolved diagnostics (Ara h 2) to refine risk, then oral food challenge if the diagnosis remains uncertain. Addresses safety: OFC is done under medical supervision with resuscitation capability. [3][1]

Domain 3: Shared decision-making (25%) — Presents the options clearly: Ara h 2 component testing now, proceed directly to oral food challenge, or continue avoidance without further testing. Explains the pros and cons of each option. Explores what matters to the mother. Agrees on a plan together. [3][4]

Domain 4: Safety-netting and follow-up (20%) — Advises that until the diagnosis is clarified, Sophie should continue to avoid peanut. Provides a written allergy action plan and an adrenaline autoinjector if the challenge confirms allergy. Arranges follow-up after the component test and/or challenge. Gives clear advice on what to do if an accidental reaction occurs before the next appointment. [1][2]

Model encounter summary

The strong candidate opens by asking Mrs Chen what she understands about the result and what worries her most. She learns that the mother's primary fear is anaphylaxis. The candidate explains that a positive SPT means Sophie's immune system has made IgE antibodies to peanut — she is sensitised — but that this does not automatically mean she will react if she eats peanut. Using a plain-language analogy, she explains that approximately half of children with a positive test tolerate the food. She states that a 6 mm wheal is in the uncertain zone — above the 3 mm positive cutoff but below the 8 mm level where nearly all children react. [3][1]

She then outlines the pathway: a blood test for Ara h 2 (the peanut component most predictive of clinical allergy), and if that is also ambiguous, a supervised oral food challenge in the hospital day unit. She explains the challenge protocol — escalating doses under observation, with resuscitation equipment and trained staff immediately available — and reassures Mrs Chen that severe reactions during challenge are uncommon. [3][2]

She asks what matters most to the mother: if the answer is certainty and the ability to include peanut safely if Sophie is not allergic, the plan is Ara h 2 testing followed by OFC. If the mother prefers to avoid further intervention, the candidate respects that while explaining the consequence: Sophie will carry an unnecessary dietary restriction. [3]

She provides a written plan, arranges the Ara h 2 test, and books a follow-up appointment. She safety-nets: avoid peanut until the result is known, and if any reaction occurs, use the action plan and call an ambulance. [1][4]

Examiner notes

This station tests three skills: (1) the candidate's ability to explain the fundamental concept that sensitisation is not clinical allergy — the single most important idea in food allergy diagnosis and the source of most overdiagnosis; (2) the candidate's knowledge of the diagnostic pathway from SPT through component testing to OFC; and (3) communication and shared decision-making with an anxious parent. [3][1]

Weak candidates tell the mother that Sophie "has a peanut allergy" based on the 6 mm wheal, or reflexively prescribe an adrenaline autoinjector without pursuing the diagnosis further. Strong candidates explain the uncertainty, present the pathway, and engage the mother in deciding how far to pursue the diagnosis. [3][2]