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Cystic fibrosis newborn screening: outcome of infants with normal sweat tests
  1. Claire Edmondson1,
  2. Christopher Grime1,
  3. Ammani Prasad2,
  4. Jacqui Cowlard3,
  5. Chinedu E C Nwokoro3,
  6. Gary Ruiz4,
  7. Colin Wallis2,
  8. Ian M Balfour-Lynn1
  1. 1Paediatric Respiratory Medicine, Royal Brompton Hospital, London, UK
  2. 2Cystic Fibrosis Unit, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
  3. 3Respiratory Medicine, Barts the Royal London Hospital, London, UK
  4. 4Child Health, King’s College Hospital, London, UK
  1. Correspondence to Dr Ian M Balfour-Lynn, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK; i.balfourlynn{at}ic.ac.uk

Abstract

Newborn babies positively screened for cystic fibrosis (CF) (high serum immunoreactive trypsin (IRT) with DNA analysis) are referred for a diagnostic sweat test, which may be normal (sweat chloride <30 mmol/L). Unless two gene mutations are identified during Newborn screening (NBS), the babies are discharged from follow-up. We wished to check that none had subsequently developed symptoms suggestive of CF. We retrospectively reviewed patient notes and contacted general practitioners of all babies with a negative sweat test, conducted in one of the four paediatric specialist CF centres in London, over the first 6 years of screening in South East England.

Of 511 babies referred, 95 (19%) had a normal sweat test. Five (5%) had CF diagnosed genetically, two of them on extended genome sequencing after clinical suspicion. Eleven (12%) were designated as CF screen positive inconclusive diagnosis (CFSPID); one of the five CF children was originally designated as CFSPID. Seventy-nine (83%) were assumed to be false-positive cases and discharged; follow-up data were available for 51/79 (65%); 32/51 (63%) had no health issues, 19/51 (37%) had other significant non-CF pathology.

These results are reassuring in that within the limitations of those lost to follow-up, CF symptoms have not emerged in the discharged children. The high non-CF morbidity in these children may relate to known causes of high IRT at birth. Clinicians need to be aware that a child can have CF despite a normal sweat test following NBS, and if symptoms suggest the diagnosis, further testing, including extended genome sequencing, is required.

  • cystic fibrosis
  • screening

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Footnotes

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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