Clinical management of children and adults with cystic fibrosis

Diagnosis

The modes of presentation are listed (box 1) because some are not well known. Overdiagnosis remains a problem. In some parts of Britain up to 10% of patients referred to regional centres with cystic fibrosis are found to have an alternative diagnosis.3 The total absence of one or more of the major features - malabsorption due to pancreatic insufficiency, chronic suppurative lung disease, and failure to thrive - should lead to caution about the diagnosis. The main reasons for these errors are a disregard of the clinical features or the lack of them, incorrect performance of the sweat test, and faulty interpretation of the results of the test. Some patients (less than 10% seen in the United Kingdom, but up to 38% in one Canadian series), have sufficient pancreatic function for normal digestion, so that even the most sophisticated direct pancreatic function testing can exclude only pancreatic insufficiency and not cystic fibrosis itself. Homozygosity for one of the recognised gene deletions clearly indicates cystic fibrosis. Unfortunately, a cystic fibrosis mutation cannot be detected in about a fifth of patients; thus, negative results in the search for homozygosity of a cystic fibrosis gene does not exclude the diagnosis. In many cases, the final diagnosis still hinges on the accurate performance and correct interpretation of the sweat test.