NORMAL SWEAT CHLORIDE VALUES DO NOT EXCLUDE THE DIAGNOSIS OF CYSTIC-FIBROSIS

Since its introduction in 1959, the sweat test has remained the ''gold standard'' diagnostic test for cystic fibrosis (CF). It is apparent t hat CF encompasses a wide spectrum of disease, from meconium ileus and severe respiratory compromise in infants to the presentation of mild pulmonary symptoms and no evidence of gastrointestinal disease in adul ts. In patients with lung disease that might otherwise be consistent w ith CF, normal sweat chloride (Cl-) values have tended to exclude the diagnosis. In this report we describe two patients from two families w ith the compound heterozygotic CF mutations Delta F508/3849 + 10 kb C --> T These patients had mild manifestations of disease, including cli nical pancreatic sufficiency (normal growth without pancreatic enzyme supplementation) and absence of azoospermia. Sweat Cl- values were in the normal range. However, both patients developed bronchiectasis, pro gressive obstructive lung disease, and colonization with Pseudomonas. The diagnosis of CF was made using nasal transepithelial voltage measu rements and genotyping. These cases emphasize the need to maintain a h igh index of suspicion of CF in atypical cases, and to pursue alternat ive diagnostic tests to confirm a diagnosis of CF suspected on clinica l grounds, despite normal sweat test results.