Celiac disease: A disorder resulting from an immune reaction to gluten, a protein found in wheat and related grains, and present in many foods. Celiac disease causes impaired absorption and digestion of nutrients through the small intestine. Symptoms include frequent diarrhea , weight loss , iron deficiency anemia, osteoporosis . A skin condition dermatitis herpetiformis can be associated with celiac disease. The most accurate test for celiac disease is a biopsy of the small bowel usually performed by an endoscopy (tube passed into the intestine through the mouth). Treatment is to avoid gluten in the diet. Medications may be used for refractory (stubborn) celiac disease.