What study can definitively diagnose celiac disease?

Celiac disease is a chronic autoimmune disorder triggered by the ingestion of gluten in genetically predisposed individuals. The definitive diagnosis of celiac disease involves demonstrating the presence of villous atrophy in the small intestine. This is achieved through a small bowel biopsy, where a tissue sample from the duodenum or jejunum is examined microscopically. The characteristic histopathological findings include flattening of the villi, hyperplasia of the crypts, and increased intraepithelial lymphocytes.

Barium contrast radiography is useful for assessing the anatomy of the gastrointestinal tract and identifying structural anomalies but does not provide information on the mucosal histology necessary for diagnosing celiac disease. The Schilling test, which evaluates vitamin B12 absorption and is primarily used to diagnose pernicious anemia rather than celiac disease, assesses the cause of vitamin B12 deficiency but does not relate to the diagnosis of celiac disease. Urinary metanephrines are markers for pheochromocytoma or other catecholamine-secreting tumors, making them irrelevant for diagnosing celiac disease.

Given this understanding, small bowel biopsy stands out as the gold standard for confirming celiac disease, making it the correct choice for diagnosis.