Counsel a family on a cow's-milk protein allergy diagnosis and formula choice — OSCE

Candidate instructions

You are the paediatric registrar in the outpatient clinic. The parents of a four-month-old boy have ten minutes with you. The baby has had blood and mucus in the stools and a flare of eczema for two weeks; he is growing well and is well in himself. The parents have read online that he has a 'dairy allergy' and have brought a goat's-milk and an 'A2' formula, asking which to switch to. They are frightened he will stop breathing if he has any milk, and that he will be allergic for life. Explain the likely diagnosis, why a planned elimination and rechallenge is the right next step, why neither goat's-milk nor A2 is the answer, what formula is appropriate, and how he will likely outgrow this. Use plain language, check understanding, and agree a clear plan. [1]

Encounter

Mother: "We think he's got a dairy allergy. The internet said to try goat's milk or A2 — we've bought both. Which one do we use? I'm terrified he'll stop breathing." [1]

Registrar: "I can see how worrying this has been, and I'm glad you've come in. Let me explain what I think is going on and then we'll agree a plan together. From the story — the blood and mucus in his poos and the eczema flare, with him growing well and well in himself — this looks like a delayed, gut-and-skin reaction to cow's-milk protein, the common and less severe type. This is very different from the sudden, alarming type that can cause anaphylaxis, so I want to reassure you first: the type your son most likely has does not cause the breathing trouble you're frightened of." [1] [2]

Father: "So we shouldn't use the goat's-milk or A2 formula?" [2]

Registrar: "That's right — neither of those, and here's why. Goat's-milk protein and A2 protein are so similar to cow's-milk protein that a baby who reacts to cow's milk will almost always react to them too, so they're not safe alternatives. The good news is we don't need to guess. The right next step is to take him off all cow's-milk protein for two to four weeks — using a special formula where the proteins are already broken down — and see whether his symptoms settle. If they do, we briefly reintroduce cow's milk to confirm it's the cause. That's how we make the diagnosis properly, rather than switching around between formulas." [2] [1]

Mother: "What formula, then? And do I need a blood test?" [1]

Registrar: "First-line we use an extensively hydrolysed formula — the proteins are broken into tiny fragments his immune system doesn't react to, and it's available on prescription. For this type of CMPA, blood tests and skin-prick tests aren't useful because they look for the immediate type of allergy, which he doesn't have; the diagnosis is made by the elimination and rechallenge we just talked about. I'll arrange dietetic input to make sure he gets everything he needs, and we'll review him at two to four weeks." [1]

Father: "Will he have this forever?" [4]

Registrar: "Almost certainly not. Most children with this type of cow's-milk allergy outgrow it in the first one to two years of life. As he grows, we'll reintroduce milk step by step, starting with well-baked milk — like a biscuit or a muffin — because the baking changes the protein in a way many children tolerate, and we climb a 'milk ladder' towards less-baked and then raw milk under our guidance. I'll give you the ladder and we'll do it together. Before you go: can you tell me, in your own words, what we're going to do over the next month?" [4] [3]

Mother: "We stop the cow's-milk formula, use the broken-down one you'll prescribe, see if his poos and skin settle, then bring him back, and you'll test whether it really was the milk by putting it back briefly. And we don't use the goat's or A2." [1]

Registrar: "That's exactly right. And the breastfeeding mother, if relevant, would do a dairy-free diet with calcium and vitamin-D support — I'll cover that if it applies to you. Here's a written plan, the prescription, and the dietitian's details. Please come back sooner if he has any sudden reaction with swelling, breathing trouble or floppiness after a feed — that would be the emergency type and we'd want him seen straight away. What questions do you still have?" [1] [2]

Marking domains

• Communication (25%): plain language, empathy, checks understanding, invites questions, and avoids jargon. [1]
• Clinical content (30%): distinguishes the delayed non-IgE-mediated from the immediate IgE-mediated phenotype, explains elimination-and-rechallenge as the diagnostic method for the non-IgE phenotype, and explains why goat's-milk and A2 are cross-reactive and inappropriate. [2]
• Reassurance and risk communication (20%): appropriately reassures on anaphylaxis risk for the non-IgE phenotype without dismissing parental fear, and sets a clear safety-net for the immediate phenotype. [1]
• Shared decision-making and plan (15%): agrees a clear, written elimination-and-rechallenge plan, names the first-line formula, and arranges dietetic input; confirms understanding by teach-back. [2]
• Prognosis and follow-up (10%): conveys the likely early resolution and outlines the milk-ladder reintroduction pathway under supervision. [4]