Introduction. Children with cystic fibrosis often have gastrointestinal symptoms despite properly selected primary therapy and pancreatic substitution therapy. A possible reason is lactase deficiency. Aim is to determine the frequency of lactase deficiency in children with cystic fibrosis and the need for appropriate dietary correction of their diets. Materials and methods. In 213 children with cystic fibrosis, during esophagogastroduodenoscopy in biopsies of the small intestinal mucosa 359 rapid tests, «Lactose intolerance quick test” were performed. According to the results of an express test, some patients diagnosed with hypolactasia to determine their tolerance to lactose underwent a glycemic load test with lactose and measured the level of fecal calprotectin to assess the level of faecal calprotectin the degree of chronic intestinal inflammation. Results. Normal lactase activity was observed in 129 (36%) biopsies studied, moderate hypolactasia in 91 (25%) biopsies, severe hypolactasia in 139 (39%) biopsies. In patients with moderate hypolactasia, according to the express test results, 20% confirmed intolerance to lactose as a result of the load test. In patients with severe hypolactasia, 72% were confirmed to be lactose intolerant, according to the results of an express test. There was no correlation between the level of calprotectin and the results of the glycemic load test with lactose. Conclusion. Lactase deficiency is observed in a significant proportion of patients with cystic fibrosis, which may be a consequence of primary adult hypolactasia and chronic intestinal inflammation. In children with cystic fibrosis with dyspeptic symptoms persisted despite correctly prescribed basic therapy and pancreatic enzymes, it is necessary to exclude lactose intolerance and prescribe a low-lactose diet.
