Background:
Ambulatory 24-hour esophageal pH measurement is the current standard for documenting the presence of gastroesophageal reflux disease (GERD). However, pathological intraesophageal acid exposure may not be detectable by conventional 24-hour pH monitoring, leading to a false negative rate of 15-30% and underestimating the true prevalence of GERD. A 48-hour pH monitoring system (BRAVO) may allow increased detection of GERD versus 24-hour pH monitoring.

Hypothesis:
Measurement of 48-hour esophageal pH will increase the sensitivity of detecting GERD compared to a 24-hour measurement.

Aim:
Determine the frequency of GERD detected over 48 hours versus a 24 hour period.

Methods:
BRAVO probe data was reviewed from 80 patients referred for symptoms of GERD between 2003-2004 at Oregon Health and Sciences University and The Oregon Clinic. Manometric or endoscopic determination of the lower esophageal sphincter (LES) was used to place the BRAVO probe 5-6cm above the LES.

Results:
71 of 80 patients had sufficient data to be included in the study (>18 hours of pH data on both day 1 and day 2). The mean age of patients was 50 years. GERD was defined by a DeMeester score > 15 and a fraction time pH<4 of >4% during a 24 hour pH period. This was demonstrated in 45 of 71 patients (63%). 25 of 71 symptomatic patients (35%) demonstrated GERD over both 24-hour periods of the study, whereas 20 of 71 patients (28%) demonstrated GERD on only one of the 24-hour periods. Of the patients with GERD over only a single 24-hour period, 65% demonstrated GERD on day 1 only and not day 2, 35% on day 2 only and not day 1 (p=0.11). Of those 20 patients with interday variability, the mean difference in DeMeester score and fraction time pH<4 was 29.3 and 7.2 respectively.

Conclusions:
There is a high degree of day-to-day variability in intraesophageal pH in GERD patients and pathological levels may be missed by a single 24-hour pH test. 48-hour pH testing increases the sensitivity of detecting GERD by as much as 28% and should therefore be considered in all patients.