Diagnostic Approach to Rule Out Malabsorption in Patients Taking Levothyroxine

Initial Assessment

The American Gastroenterological Association recommends checking thyroid function tests (TSH, free T4) to assess the degree of hypothyroidism 3

The European Society for Clinical Nutrition and Metabolism suggests that antiendomysium antibody testing should be performed as the first-line test for celiac disease, followed by upper gastrointestinal endoscopy with distal duodenal biopsies if negative but malabsorption is still suspected 1, 2
The American Gastroenterological Association recommends upper gastrointestinal endoscopy with distal duodenal biopsies to assess for small bowel enteropathies 1

Celiac disease is the most common small bowel enteropathy in European populations, according to the European Society for Clinical Nutrition and Metabolism 1, 2
The American Gastroenterological Association identifies inflammatory bowel disease, chronic diarrhea, and post-surgical conditions as common causes of levothyroxine malabsorption 4

The American Gastroenterological Association advises against relying solely on stool fat measurement, which has several limitations, including difficulty in collecting complete samples, lack of quality control, and limited diagnostic information 1