Exocrine pancreatic function testing in patients with cystic fibrosis and pancreatic sufficiency: a correlation study

Most patients with cystic fibrosis (CF) have pancreatic insufficiency; however, 15% of the patients are pancreatic sufficient (PS). Several laboratory tests have been developed to distinguish between pancreatic insufficiency and PS. The gold standard to determine pancreatic function apart from direct pancreatic stimulation test is the 72-hour fecal fat excretion, expressed as coefficient of fat absorption (CFA). The aim was to test the correlation between 2 other tests, fecal elastase-1 and serum immunoreactive trypsinogen (IRT), as compared with fecal fat excretion.

21 patients with CF-PS performed the 3 tests of fecal fat excretion, fecal elastase-1, and IRT. Correlation between the tests was evaluated by the kappa statistics test, sensitivity and specificity, and positive and negative predictive values.

CFA was abnormal in 5 patients, elastase was <200microg/g in 4 patients, and IRT was <20 ng/mL in 2 patients. The correlation between CFA and IRT was negative(kappa=-0.154), and between CFA and fecal elastase-1 was poor (kappa=0.213). The sensitivity, specificity, and positive and negative predictive values of IRT versus CFA were 0%, 88%, 0%, and 78%, and for fecal elastase-1 were 40%, 81%, 40%, and 81%, respectively.

In CF-PS, poor correlation was found between IRT, fecal elastase-1, and CFA, therefore neither fecal elastase-1 in the stool nor IRT in the serum reaches the sensitivity or the specificity of the fecal fat excretion. Thus, fecal fat excretion is required in patients with CF for evaluation of pancreatic function.