Twenty-four-hour esophageal pH monitoring has often been used as the most reliable examination for making diagnosis of gastroesophageal reflux (GER). Several pH scores, however, are composed of different cut off value, examination time, and scoring parameters. Moreover, the majority of numerous data obtaining in 24 hours is not employed in the scores. The pH scores consist of only several percent of the data confined to below pH 4. pH histograms seem to be useful as a supplement of the pH score. The histograms can be classified into 6 types, including miscellaneous type. The normal type has a steep peak with a short tail which never reaches below pH 4. The GER type shows a flattened pattern with a long tail toward pH 1. The intermediate type is characterized by symmetric distribution with a moderate tail reaching the area of pH 3 to 4, and appears to be normal, although the pH score indicates mild abnormality when the cut off value is settled at pH 4. 0- The cut off value in the pH score should be taken at 3. 6 rather than 4. 0. The long tail type is similar to the normal type with the exception of a low and long tail extending to below pH 2, which implies good esophageal clearance. The pseudo-GER type has a lower tail than in the GER type. The pH histogram represents detail of whole pH state, contrary of the pH score which refers only the reflux episodes. This may serve further advance in pathophysiological studies of GER.
