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 challeng e. In spite of the availability of different methods such as genetic analys is and measurements of nasal potential difference, uncertainty in diagnosin g cystic fibrosis (CF) in some patients still exists. Neonates with CF have high serum lipase levels, which decline over time in pancreatic-insufficie nt patients, whereas pancreatic-sufficient patients demonstrate high serum lipase levels beyond infancy. Because patients with borderline or normal sw eat test are almost always pancreatic sufficient, this study was aimed to a ssess whether serum lipase levels may be of help rn establishing the diagno sis of CF in these patients. Serum lipase levels were measured in 100 CF pa tients and in 17 healthy individuals. Patients were grouped according to th eir genotype. Group A patients (n = 70) carried two mutations previously fo und to be associated with a pathologic sweat test and pancreatic insufficie ncy (Delta F508, W1282X, G542X, N1303K, S549R). Group B (n = 30) were compo und heterozygote patients who carried one mutation known to cause mild dise ase with borderline or normal sweat tests and pancreatic sufficiency (384910kb 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 b etween groups. The distribution of lipase levels was significantly differen t 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) o f Group A and C, respectively. Lipase levels were found to be inversely rel ated 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 wi th borderline sweat tests and high lipase levels. the diagnosis of CF shoul d be considered. Pediatr Pulmonol, 2000; 30:320-323, 2000 Wiley-Liss Inc.