Thursday, June 7
Esophageal acid testing is considered a "gold standard" for diagnosing GERD. As discussed above, the reflux of acid is common in the general population. However, patients with the symptoms or complications of GERD have reflux of more acid than individuals without the symptoms or complications of GERD. Moreover, normal individuals and patients with GERD can be distinguished fairly well from each other by the amount of time that the esophagus contains acid.
The amount of time that the esophagus contains acid is determined by a test called a 24-hour esophageal ph test. (Ph is a mathematical way of expressing the amount of acidity.) For this test, a small tube (catheter) is passed through the nose and positioned in the esophagus. On the tip of the catheter is a sensor that senses acid. The other end of the catheter exits from the nose, wraps back over the ear, and travels down to the waist, where it is attached to a recorder. Each time acid refluxes back into the esophagus from the stomach, it stimulates the sensor and the recorder records the episode of reflux. After a 20 to 24 hour period of time, the catheter is removed and the record of reflux from the recorder is analyzed.
There are problems with using ph testing for diagnosing GERD. Despite the fact that normal individuals and patients with GERD can be separated fairly well on the basis of ph studies, the separation is not perfect. Therefore, some patients with GERD will have normal amounts of acid reflux and some patients without GERD will have abnormal amounts of acid reflux. It requires something other than the ph test to confirm the presence of GERD, for example, typical symptoms, response to treatment, or the presence of complications of GERD.
Ph testing has uses in the management of GERD other than just diagnosing GERD. For example, the test can help determine why GERD symptoms do not respond to treatment. Perhaps 10 to 20 percent of patients will not have their symptoms substantially improved by treatment for GERD. This lack of response to treatment could be caused by ineffective treatment. This means that the medication is not adequately suppressing the production of acid by the stomach and thereby is not reducing acid reflux. Alternatively, the lack of response can be explained by a wrong diagnosis of GERD. In both of these situations, the ph test can be very useful. If testing reveals substantial reflux of acid while medication is continued, then the treatment is ineffective and will need to be changed. If testing reveals good acid suppression with minimal reflux of acid, the diagnosis of GERD is likely to be wrong and other causes for the symptoms need to be sought.
Ph testing also can be used to help evaluate whether reflux is the cause of symptoms (usually heartburn). To make this evaluation, while the 24-hour ph testing is being done, patients record each time they have symptoms. Then, when the test is being analyzed, it can be determined whether or not acid reflux occurred at the time of the symptoms. If reflux did occur at the same time as the symptoms, then reflux is likely to be the cause of the symptoms. If there was no reflux at the time of symptoms, then reflux is unlikely to be the cause of the symptoms.
Lastly, ph testing can be used to evaluate patients prior to endoscopic or surgical treatment for GERD. As discussed above, some 20 % of patients will have a decrease in their symptoms even though they don't have GERD (the placebo effect). Prior to endoscopic or surgical treatment, it is important to identify these patients because they are not likely to benefit from the treatments. The ph study can be used to identify these patients because they will have normal amounts of acid reflux.
A newer method for prolonged measurement (48 hours) of acid exposure in the esophagus utilizes a small, wireless capsule that is attached to the esophagus just above the LES. The capsule is passed to the lower esophagus by a tube inserted through either the mouth or the nose. After the capsule is attached to the esophagus, the tube is removed. The capsule measures the acid refluxing into the esophagus and transmits this information to a receiver that is worn at the waist. After the study, usually after 48 hours, the information from the receiver is downloaded into a computer and analyzed. The capsule falls off of the esophagus after 3-5 days and is passed in the stool. (The capsule is not reused.) The advantage of the capsule over standard ph testing is that there is no discomfort from a catheter that passes through the throat and nose. Moreover, with the capsule, patients look normal (they don't have a catheter protruding from their noses) and are more likely to go about their daily activities, for example, go to work, without feeling self-conscious. Capsule ph testing is expensive. Sometimes the capsule does not attach to the esophagus or falls off prematurely. For periods of time the receiver may not receive signals from the capsule, and some of the information about reflux of acid may be lost. Occasionally there is pain with swallowing after the capsule has been placed. Use of the capsule is an exciting use of new technology, but with its inherent problems and lack of widespread use and evaluation, it is not yet clear what its role should be.