Final answer:
The barium enema should be scheduled last among the GI diagnostic studies because barium can obscure other tests like ultrasound, CT scans, and colonoscopies due to residue left in the colon.
Step-by-step explanation:
When a nurse is scheduling diagnostic studies for the gastrointestinal (GI) system, the timing of each study can be important due to how they might impact each other. Among the options listed, the barium enema should generally be scheduled last. This is because a barium enema involves introducing barium sulfate into the colon to outline the intestine on X-ray images. Barium is a contrast material that can obscure other diagnostic tests such as ultrasounds, computed tomography (CT scans), or endoscopic procedures like a colonoscopy. A barium enema can leave residue in the colon, which might interfere with the clarity of subsequent imaging tests or the direct visual inspection required in a colonoscopy.
It is advisable to schedule other studies such as ultrasound, CT scans without barium, or colonoscopy prior to a barium enema. This allows for accurate visualization and diagnosis without the interference of barium. Consequently, the nurse should take care to arrange the tests in an order that ensures the most precise diagnostic information can be gathered with minimal need for repeat procedures.