What is the best initial test for diagnosing celiac disease in a patient with inflammatory bowel symptoms?

The serum IgA tissue transglutaminase (tTG-IgA) antibody test is the recommended first-line serological test for diagnosing celiac disease in symptomatic individuals. Tissue transglutaminase is the primary autoantigen in celiac disease, and elevated IgA antibodies against it are highly sensitive and specific for the condition. This test is non-invasive, cost-effective, and widely available, making it the best initial approach when celiac disease is suspected based on symptoms such as diarrhea, abdominal pain, bloating, malabsorption, or weight loss. Colonoscopy with biopsy (option 366499) examines the large intestine and is more appropriate for inflammatory bowel disease such as Crohn's disease or ulcerative colitis; celiac disease affects the small intestine and is confirmed by small bowel (duodenal) biopsy via upper endoscopy, not colonoscopy. MRI of the abdomen (option 366500) is not a diagnostic tool for celiac disease and would not detect intestinal villous atrophy. Stool sample analysis (option 366501) can help identify infections or assess for malabsorption but is not a specific or definitive test for celiac disease. Confirmatory diagnosis after positive serology involves upper endoscopy with duodenal biopsy showing villous atrophy.