What is the most appropriate next investigation for a patient with iron deficiency anemia following an upper gastrointestinal endoscopy showing a duodenal ulcer?

In this scenario, the patient has been diagnosed with iron deficiency anemia and has already undergone an upper gastrointestinal endoscopy that revealed a duodenal ulcer. Given the context, the most appropriate next investigation is a colonoscopy.

Iron deficiency anemia can often indicate bleeding or malignancy, particularly when there is no clear source of blood loss from the upper gastrointestinal tract. Even though the duodenal ulcer may explain some blood loss, it is essential to investigate further to rule out other potential causes of the anemia.

Colonoscopy allows for direct visualization of the lower gastrointestinal tract. It is particularly indicated in this context to check for any lesions, polyps, or sources of bleeding that may be present in the colon, especially since any significant gastrointestinal bleeding could contribute to the anemia. This is especially important in older patients or those with risk factors for colorectal cancer.

While other options like a CT scan or repeat upper endoscopy may provide additional information, they are not as directly relevant in investigating the potential causes of the iron deficiency anemia related to lower gastrointestinal sources. A CT scan may visualize structures but does not allow for direct assessment of the colonic mucosa. A repeat endoscopy might not provide new information since the source has presumably already been identified with the duoden