Abstract:

Patients with normal or borderline sweat tests present a diagnostic challenge. In spite of the availability of genetic analysis and measurement of nasal potential difference, there is still uncertainty in diagnosing cystic fibrosis in some patients. CA 19–9 is a tumor-associated antigen whose levels were previously found to be elevated in some cystic fibrosis patients. We investigated whether serum CA 19–9 levels can contribute to establishing the diagnosis of cystic fibrosis in patients with a borderline sweat test, and evaluated the influence of different clinical variables on CA 19–9 levels. Serum CA 19–9 levels were measured in 82 cystic fibrosis patients grouped according to their genotype and in 38 healthy individuals. Group A included 50 patients who carried two mutations previously found to be associated with a pathological sweat test and pancreatic insufficiency (ΔF508, W1282X, G542X, N1303K, and S549R). Group B included 13 compound heterozygote cystic fibrosis patients who carried one mutation known to cause mild disease with a borderline or normal sweat test and pancreatic sufficiency (3849+10kb C→T, 5T). Group C included 38 normal controls. Nineteen cystic fibrosis patients carried at least one unidentified mutation. An association between CA 19–9 levels and age, pulmonary function, pancreatic status, sweat chloride, previous pancreatitis, serum lipase, meconium ileus, distal intestinal obstruction, liver disease, and diabetes was investigated. The distribution of CA 19–9 levels was significantly different between the three groups (p<0.01); high CA 19–9 levels were found in 60% (30/50) of group A patients and in 46.6% (6/13) of group B patients, but in only 5.2% (2/38) of the controls. CA 19–9 levels were inversely related to forced expiratory volume in 1 s, while no association was found with the other clinical parameters examined. Our findings suggest that the serum CA 19–9 in cystic fibrosis patients originates in the respiratory system, and has a useful ancillary role, particularly when diagnostic uncertainty exists. Hence, the diagnosis of cystic fibrosis should be considered in patients with borderline sweat tests and high CA 19–9 levels, but normal levels do not exclude cystic fibrosis.