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Diagnosing CF: sweat, blood and years
  1. J S Elborn1,
  2. J M Bradley2
  1. 1Respiratory Medicine Group, Queen’s University, Belfast, UK
  2. 2Health and Rehabilitation Sciences Research Institute, University of Ulster, UK
  1. Correspondence to:
    Professor J S Elborn
    Professor of Respiratory Medicine, Queen’s University, Belfast and Director of the Northern Ireland Adult Cystic Fibrosis Centre, City Hospital, Belfast BT9 7AB, UK; stuart.elborn{at}

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Use of algorithms for the diagnosis of CF

The diagnosis of cystic fibrosis (CF) is usually straightforward. The accepted criteria for the diagnosis of CF is one phenotypic characteristic of CF (such as lung disease or pancreatic malabsorption), or a positive neonatal screening result, or a positive history of CF in a sibling plus a raised sweat chloride level, positive nasal potential difference (PD) test, or two mutations in the CFTR gene.1 In countries with neonatal screening the diagnosis is made in most cases using either an immunoreactive trypsinogen (IRT) test on a heel prick blood sample or direct detection of genetic mutations.2 Missed cases (false negatives) from screening are almost all pancreatic sufficient with minimal lung disease, and may have a consequent delay in diagnosis.2 In countries which do not yet have neonatal screening for CF, most children present in the first year of life with failure to thrive, recurrent respiratory infections, or both.2 For such children a sweat test is the most important investigation to confirm the diagnosis. Some patients also present with clinical disease later in childhood and into adult life and diagnosis can be more difficult for a number of reasons.

In late diagnosed patients there is a wider range of presenting phenotypes in addition to the common presentations with respiratory infection and pancreatic malabsorption.3 Some present with single organ pulmonary disease (bronchiectasis), pancreatitis, severe sinusitis, or infertility. The explanation for this is that some mutations of the CFTR gene are associated with an atypical phenotype, usually with less severe lung disease. Over 1000 …

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