ABSTRACT.Objective. Exocrine pancreatic function in patients with cystic fibrosis (CF) can be evaluated by direct and indirect tests. In pediatric patients, indirect tests are preferred because of their less invasive character, especially in CF patients with respiratory disease. Fecal tests are noninvasive and have been shown to have a high sensitivity and specificity. However, there is no comparative study in CF patients. Therefore, the aim of the present study was to compare the sensitivity and the specificity of the fecal elastase-1 (E1) test with the fecal chymotrypsin (ChT) test in a large cohort of CF patients and healthy subjects (HS).Design. One hundred twenty-three CF patients and 105 HS were evaluated. In all subjects, E1 concentration and ChT activity were measured. In the CF group, fecal fat excretion was also determined. The sensitivity and specificity of the fecal E1 test and ChT test were compared.Results. With a cutoff level of 3 U/g, ChT specificity in HS was similar to that of E1, but E1 sensitivity in CF patients was significantly higher (90.2% vs 81.3%). With a cutoff level of 6 U/g, ChT and E1 sensitivity in CF patients was identical, but E1 specificity in HS was again significantly higher (98.1% vs 90.5%). In all CF patients with severe steatorrhea (>15 g/d), E1 concentrations were abnormal and ChT activity was lower than 3 U/g. In contrast, in pancreatic-sufficient patients and patients with mild steatorrhea (<15 g/d), the E1 sensitivity was significantly higher compared with ChT (69.2% vs 41.0%).Conclusions. The fecal E1 test is superior to fecal ChT determination in the assessment of CF pancreatic involvement in pancreatic-sufficient patients and those patients with mild steatorrhea. Pediatrics 2002;110(1). URL: http://www.pediatrics.org/cgi/content/full/110/1/e7; fecal elastase-1, fecal chymotrypsin, exocrine pancreatic function, cystic fibrosis.

The decline of EPF in patients with CF appears more frequently during the first months and years of life. However, late PS to pancreatic-insufficient (PI) conversion is also possible. The appearance of maldigestion is preceded by the decrease of fecal E1 concentration. Thus, the fecal E1 test is a helpful screening tool for the longitudinal assessment of declining EPF in PS patients with CF to demonstrate pancreatic deterioration. In suspected patients, fecal fat excretion should be assessed.

Patients who carry two 'severe' mutations develop pancreatic insufficiency, whereas those who carry at least one 'mild' usually remain pancreatic sufficient. However, the presence of one mild mutation does not exclude pancreatic insufficiency.

In clinical practice, instead of a single best cut-off level for the E1 test, we suggest using a range of values (160-200 microg/g). The presence of different best cut-off levels within countries is a practical consequence of the different distribution of pancreatic function.

Exogenous applied pancreatic enzymes, dose- and time-dependently inhibited endogenous pancreatic secretion. The obtained results strongly support the existence of a protease mediated feedback mechanism in humans.