Serum lipase levels as a diagnostic marker in cystic fibrosis patients with normal or borderline sweat tests

Patients with normal or borderline sweat test present a diagnostic challenge. In spite of the availability of different methods such as genetic analysis and measurements of nasal potential difference, uncertainty in diagnosing cystic fibrosis (CF) in some patients still exists. Neonates with CF have high serum lipase levels, which decline over time in pancreatic-insufficient patients, whereas pancreatic-sufficient patients demonstrate high serum lipase levels beyond infancy. Because patients with borderline or normal sweat test are almost always pancreatic sufficient, this study was aimed to assess whether serum lipase levels may be of help in establishing the diagnosis of CF in these patients. Serum lipase levels were measured in 100 CF patients and in 17 healthy individuals. Patients were grouped according to their genotype. Group A patients (n = 70) carried two mutations previously found to be associated with a pathologic sweat test and pancreatic insufficiency (ΔF508, W1282X, G542X, N1303K, S549R). Group B (n = 30) were compound heterozygote patients who carried one mutation known to cause mild disease with borderline or normal sweat tests and pancreatic sufficiency (3849+10kb C→T, 5T). Group C included 17 healthy controls. Serum lipase levels ranged between 2 and 104.4 U/L (mean ± SD 16.9 ± 14.7), 6.1-200 U/L (mean ± SD 53.9 ± 47.9), and 8.5-27.8 U/L (mean ± SD 16.9 ± 5.1) in Groups A, B, and C, respectively, with some overlapping between groups. The distribution of lipase levels was significantly different in Group B vs Groups A and C (P< 0.01). High lipase levels were found in 63.3% (19/30) of Group B patients, but in only 4.3% (3/70) and 0% (0/17) of Group A and C, respectively. Lipase levels were found to be inversely related to sweat chloride concentrations (r = -0.19, P < 0.05). Patients with borderline or normal sweat tests had high lipase levels, whereas low lipase levels were associated with pathologic sweat tests. Our findings indicate that the serum lipase level is genetically determined and that it has a useful role in the diagnosis of CF. Thus, in patients with borderline sweat tests and high lipase levels, the diagnosis of CF should be considered. (C) 2000 Wiley-Liss, Inc.