The Heidelberg test is a medical diagnostic test used in the diagnosis of hypochlorhydria, i.e. insufficient hydrochloric acid in the stomach.
When performing the Heidelberg test, the patient swallows a small electronic device about the size of a vitamin capsule. This device tracks acid levels in the stomach as the patient swallows small amounts of baking soda, which neutralises the hydrochloric acid in the stomach. If the acid level does not return to normal after the baking soda is swallowed, the patient has hypochlorhydria.
The capsule is attached to a long thread to control the position of the capsule in the stomach. After the pH measurements have been recorded, the capsule may be allowed to pass into the intestine and be expelled through the rectum. The testing procedure may take 1–2 hours.