Acid-related tests are being used to ascertain the effectiveness of acid-blocking drugs. All require nasogastric or nasoesophageal intubation. Complications are very rare. Patients must have nothing by mouth (npo) after midnight. Ambulatory 24-h esophageal pH monitoring is currently the best available test for quantifying esophageal acid exposure. The principal indications are (1) to document excessive acid exposure in patients without endoscopic evidence of esophagitis, and (2) to evaluate the effectiveness of medical or surgical treatments. A thin tube containing a pH probe is positioned 5 cm above the lower esophageal sphincter. The patient records symptoms, meals, and sleep for 24 h. Esophageal acid exposure is defined by the percentage of the 24-h recording time that the pH is < 4.0. Values > 3.5% are considered abnormal. However, symptoms may not correlate with acid exposure or the presence of esophagitis. This may be because symptoms may result from nonacidic as well as acidic refluxate.

In 2001, the FDA approved the Given Diagnostic Imaging System: a 11 x 26 mm capsule weighing only 4 gms (about 1/7th of an ounce) and containing a color video camera and wireless radiofrequency transmitter, 4 LED lights, and enough battery power to take 50,000 color images during an 8-hour journey through the digestive tract. About the size of a large vitamin, the capsule is made of specially sealed biocompatible material that is resistant to stomach acid and powerful digestive enzymes. Another name for this new technique is Wireless Capsule Endoscopy.
Patients report that the video capsule is easier to swallow than an aspirin. It seems that the most important factor in ease of swallowing is the lack of friction. The capsule is very smooth, enabling it to slip down the throat with just a sip of water. After the Given M2A capsule is swallowed, it moves through the digestive track naturally with the aid of the peristaltic activity of the intestinal muscles.
The patient comfortably continues with regular activities throughout the examination without feeling sensations resulting from the capsule's passage. During the 8 hour exam, the images are continuously transmitted to special antenna pads placed on the body and captured on a recording device about the size of a portable Walkman which is worn about the patient's waist. After the exam, the patient returns to the doctor's office and the recording device is removed. The stored images are transferred to a computer PC workstation where they are transformed into a digital movie which the doctor can later examine on the computer monitor. Patients are not required to retrieve and return the video capsule to the physician. It is disposable and expelled normally and effortlessly with the next bowel movement.
This technique is relatively new, but numerous reports have already demonstrated cases in which the Given videocapsule was able to make a diagnosis not seen by conventional studies.