Low sweat electrolytes in a patient with cystic fibrosis.

A patient with the clinical syndrome of cystic fibrosis characterized by chronic pulmonary disease, infection with mucoid Pseudomonas aeruginosa, sinusitis, nasal polyposis, abnormal pancreatic bicarbonate response to secretin stimulation, but normal levels of trypsin and chymotrypsin in the duodenal drainage, and a sibling with autopsy-documented cystic fibrosis, is described. Sweat chloride ranged from 20 to 44 meq/liter and sweat sodium from 36 to 55 meq/liter. Immunoglobulin deficiency, alpha 1-antitrypsin deficiency, tuberculosis and abnormalities of ciliary ultrastructure were excluded. Review of sweat electrolytes in 213 patients with cystic fibrosis revealed that patients with normal pancreatic enzyme release have significantly lower sweat sodium and chloride concentrations (p < 0.0005) than do patients with pancreatic insufficiency. Chronic pulmonary disease, pancreatic insufficiency and elevated levels of sweat electrolytes comprise the classic diagnostic triad for cystic fibrosis. The expression of these features may be variable, but the sweat test remains the cardinal laboratory confirmation of the diagnosis. Over 98 percent of patients with cystic fibrosis have sweat chloride values greater than 60 meq/liter, 1 to 2 percent between 50 and 60 meq/liter, and only about one in 1,000, like our patient, less than 50 meq/liter. Patients with cystic fibrosis with borderline sweat chloride values frequently have chronic pulmonary disease but intact pancreatic enzyme release. In such patients, family history, ancillary clinical features and systemic exclusion of other syndromes assume special diagnostic importance.