Background There are an increase number of children with genetically confirmed lactase deficiency (LD) in recent years, which may be a casual diagnostic finding without clinical manifestations. Lactase deficiency (hypolactasia) can be genetically determined or occur secondarily in the background of diseases of the small intestine.

The purpose of the study: to study the incidence of lactose malabsorption in children with various diseases of digestive tract.

patients and methods. The study involved 67 children at the age from 1 to 18 years: 35 girls and 32 boys without clinical signs of LD. The pathology of digestive tract was presented with: cystic fibrosis (n=30), constipation (n=3), malabsorption (n=11), inflammatory bowel disease (n=17) and gastroduodenitis (n=6). In all children was performed esophagogastroduodenoscopy with biopsy of the small intestine. Then the research of the mucous membrane bioptats of the jejunum was conducted by Lactose Intolerance quick test.

Results Among all surveyed children, the most prominent impairment was observed in patients with hereditary-caused deficiency of the exocrine pancreatic function, manifested as cystic fibrosis. Severe hypolactasia (HL) identified in 20%, moderate LD in 27% and normolactasia (NL) in 53% of patients.

In children with upper gastrointestinal tract (malabsorption syndrome) disorders severe HL were observed in 18% of patients, moderate LD – 36%, NL – 46%. As to gastroduodenitis we got the follows data: moderate LD and NL in equal proportions (50%).

In pathology of the lower gastrointestinal tract severe HL was observed in 2 times more (24%) compared to pathology of the upper parts, medium (moderate) in 41% and in children with inflammatory colon diseases (Crohn’s Disease, ulcerative colitis) NL were identified in 35%. In all children with functional pathology of the lower gastrointestinal tract the NL was noted.

Conclusions Every second child with digestive tract pathology has lactase deficiency that worsen the severity and course of the main disease and not always amenable to conventional therapy. The results indicate that the underestimated role of LD in the course and treatment of the underlying disease, and this problem requires further study.