What are the risks, costs, and downsides of scintigraphy or motility capsules?

The short version: both tests expose you to radiation or a swallowed device with known retention risk, and neither has been proven to change long-term outcomes in a controlled trial.

Scintigraphy for gastric emptying involves eating a radioactive meal (typically technetium-99m) and lying under a gamma camera for several hours. The radiation dose is low, about the same as a chest X-ray, but it is still ionizing radiation delivered to a healthy person for a diagnostic test. The 2018 review [4] calls scintigraphy the "gold standard" for gastroparesis, but that label comes from consensus, not from a trial showing it improves symptoms or survival. The 1992 Mayo review [1] describes the method in detail and notes it was funded by NIH and the Mayo Foundation, not by a device manufacturer, which is better than most. Still, no study in your evidence compares scintigraphy to no testing in a randomized design.

The wireless motility capsule (SmartPill) avoids radiation but carries a real risk: the capsule can get stuck. The 2018 pediatric review [7] explicitly mentions "potential capsule retention risk in children" and says pediatric data is scarce. The capsule measures pH, temperature, and pressure as it travels, but the 2012 review [3] reports a median small bowel transit time of 350 minutes in only 9 subjects, which tells you the reference ranges are built on tiny samples. The capsule costs hundreds of dollars and requires the patient to swallow a device the size of a large vitamin.

Both tests share a deeper problem. They measure transit time, but transit time correlates poorly with symptoms. The 2018 review [4] states plainly: "discordance between symptoms and objective delay." A patient can have normal transit and severe symptoms, or delayed transit and no symptoms. The test tells you a number, not what to do about it. The 2020 review [6] on functional constipation recommends a stepwise approach starting with history and simple laxatives, not transit testing, for most patients.

My call: neither test has been shown in a controlled study to improve patient outcomes over clinical assessment alone. The evidence for their routine use is thin. Confidence: moderate.