Explain a positive newborn cystic fibrosis screen to worried parents — OSCE

Candidate instructions

You are the paediatric registrar in a general clinic. A 5-week-old girl has had a positive newborn bloodspot screen for cystic fibrosis (raised trypsinogen and one ΔF508 mutation). She is well, feeding and growing normally. Her parents have ten minutes with you before her referral to the CF centre. They want to understand, in plain language: (1) what the positive screen means; (2) whether their daughter definitely has CF; (3) what the sweat test involves; and (4) what happens next. Explain with empathy, check understanding, and agree a clear plan. [1]

Encounter

Mother: "They said the screen was positive. Does that mean she has cystic fibrosis?" [2]

Registrar: "I can see how frightening that word is, so let me be clear from the start. A positive screen is a signal that we need to do more tests — it is not a diagnosis. The screen is deliberately set to catch every baby who might have cystic fibrosis, which means many babies with a positive screen turn out not to have it. We now need a confirming test to find out for certain, and I will explain exactly how that works." [2] [1]

Father: "But you found a gene change. Doesn't that prove it?" [1]

Registrar: "That is a really good question. Cystic fibrosis is caused by changes in a gene called CFTR, and a child needs two faulty copies — one from each parent — to have the condition. The screen found one copy in your daughter, which means she carries it, but one copy alone does not cause the disease. To diagnose CF we need proof that the gene is not working, and the main way we check that is the sweat test." [1] [2]

Mother: "What is a sweat test? It sounds strange." [3]

Registrar: "It is simple and painless for her. We put a small, harmless medicine on a patch of skin, usually on the arm, and use a tiny, gentle electrical current to make that patch sweat. We collect the sweat and measure how much salt is in it, because in cystic fibrosis the sweat is much saltier than normal. A low salt level makes CF very unlikely, a high level confirms it, and an in-between result means we do a bit more testing to be sure." [3] [1]

Father: "How soon will we know, and where is it done?" [1]

Registrar: "We do the sweat test at the specialist children's cystic fibrosis centre, where the team does it to a very high standard, and we will arrange that appointment quickly rather than leaving you waiting. If the result is clear we will know soon after; if it is in-between we will add a fuller look at the gene. Diagnosing early genuinely matters — babies found early and looked after by the CF team grow better than those found late — so we want to move promptly." [4] [1]

Mother: "And if it does turn out to be cystic fibrosis?" [1]

Registrar: "If it is confirmed, she would be looked after by a whole team — chest and gut specialists, a dietitian, a physiotherapist and nurses — and there is a great deal we can do to keep her well and growing. We would also talk with you about what it means for the family and offer genetic counselling. But we are getting ahead of ourselves — first let us confirm, and whatever the result, you will not be left without support." [1] [2]

Father: "Thank you. That is much clearer." [1]

Registrar: "I will give you written information and the CF centre's contact details, and I will make sure the sweat test is booked. To check I have explained it well — could you tell me, in your own words, what a positive screen means and what the sweat test is for?" [2]

Examiner debrief

A strong candidate opens by separating a positive screen from a diagnosis, normalises the parents' fear, and explains that many screen-positive babies do not have CF. They explain, in plain language, that CF needs two faulty CFTR copies and that one mutation makes a carrier, so a confirming test of gene function is needed. They describe the sweat test accurately and reassuringly as painless, name the sweat centre and the interpretation in broad terms, and stress prompt referral, citing the benefit of early diagnosis on growth. They avoid both premature alarm and false reassurance, handle the possibility of an equivocal result honestly, offer written information, genetic counselling and support, and check understanding with teach-back. Pitfalls include telling the parents the baby "has CF" on a screen alone, dismissing the result as nothing, describing the sweat test inaccurately or painfully, and failing to arrange timely confirmatory testing. [1] [2] [3]