A 3-year-old boy has bulky stools. What investigation is most likely to lead to a diagnosis?

In a 3-year-old boy presenting with bulky stools, the investigation most likely to lead to a diagnosis is the test for anti-endomysial antibodies. This is particularly relevant given the presentation of bulky stools, which can suggest malabsorption.

The presence of anti-endomysial antibodies is strongly associated with celiac disease, a condition wherein the ingestion of gluten leads to damage in the small intestine, affecting absorption of nutrients and resulting in symptoms such as diarrhea, bulky stools, and poor growth. In young children, celiac disease can manifest in a variety of gastrointestinal symptoms, including abdominal pain, bloating, and the production of large, greasy stools that float, indicating malabsorption of fats.

While the other tests mentioned can be useful in specific contexts, they do not correspond to the clinical suspicion raised by the symptom of bulky stools. For instance, the sweat chloride test is primarily used for diagnosing cystic fibrosis, which may have some similar gastrointestinal presentation but is less likely to be the primary concern with this symptom alone. Liver function tests are pertinent in assessing liver conditions but would not specifically address the cause of bulky stools. An abdominal ultrasound is useful for evaluating structural abnormalities but does not directly investigate the malabsorption indicated by the symptom