Pancreatic insufficiency in cystic fibrosis (CF) is associated with more severe disease and requires replacement therapy. Outcome measures such as growth and number of stools, frequency of abdominal pain, and flatulence have often been used to identify pancreatic-insufficient patients and to adjust the dose of replacement enzymes. Unfortunately, some patients with CF are misclassified, and approximately 9% do not receive therapy appropriate for their pancreatic exocrine functional status. Growth, number of stools, frequency of abdominal pain, and flatulence cannot be used to adjust enzyme doses.