Edmondson C, et al. - In view of the observation that a diagnostic sweat test is performed among newborn babies positively screened for cystic fibrosis (CF) (high serum immunoreactive trypsin (IRT) with DNA analysis), which may be normal (sweat chloride <30 mmol/L), and these babies are discharged from follow-up unless two gene mutations are identified during Newborn screening (NBS), researchers conducted a retrospective review of 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, to determine that none of the discharged newborns subsequently developed symptoms suggestive of CF. The discharged children did not display CF symptoms. They observed a high non-CF morbidity in these children, that may relate to known causes of high IRT at birth. Clinicians are suggested to be aware of the fact 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.