Celiac Disease with Patchy Involvement or Early Disease: High tissue transglutaminase antibodies (TTG) are a hallmark of celiac disease. Even with normal histopathology, celiac disease is a strong consideration, especially if the biopsy samples did not capture the affected areas due to the patchy nature of the disease or if the disease is in its early stages before significant histological changes occur.

Non-Celiac Gluten Sensitivity (NCGS): Although the exact mechanisms and diagnostic criteria for NCGS are still under debate, some individuals with NCGS may have elevated TTG antibodies without the characteristic histological findings of celiac disease.
Autoimmune Disorders: Certain autoimmune conditions, such as type 1 diabetes, autoimmune thyroid disease, or rheumatoid arthritis, can be associated with elevated TTG antibodies, even in the absence of celiac disease.

IgA Deficiency: This is the most common primary immunodeficiency. Individuals with IgA deficiency may have false-negative results for IgA-based TTG tests but could still have celiac disease, making it crucial to also test for IgG-based antibodies in such cases.
Gastrointestinal Lymphoma: Although rare, gastrointestinal lymphoma can be associated with celiac disease and may not always present with abnormal histopathology initially.

Eosinophilic Gastroenteritis: A rare condition characterized by eosinophilic infiltration of the gastrointestinal tract, which can sometimes present with elevated TTG antibodies.
Crohn's Disease or Ulcerative Colitis with Elevated TTG: Inflammatory bowel diseases can occasionally have elevated TTG antibodies, although this is less common and the primary diagnosis would typically be based on other clinical, endoscopic, and histological findings.