Gastro-oesophageal reflux disease (GORD) is widely defined as a condition that develops when the refluxed material of the stomach content causes troublesome symptomatology and/or complications.1 The 24-hour multichannel intraluminal impedance and pH monitoring (MII-pH) is presently the gold standard diagnosis tool, but it is invasive and expensive. There is, however, no suitable, non-invasive substitute diagnostic method applicable for GORD diagnosis in clinical practice.
Exhaled breath condensate (EBC)2 and saliva3 are two easily obtained, non-invasive samples that bear promise in monitoring patients suffering from GORD. The aim of this study was to investigate the prospects of these samples in non-invasive diagnostic approaches to GORD. We compared the pH and total ionic profile of EBC, analysed by capillary electrophoresis with contactless conductometric detection, MII-pH, and salivary Peptest in a group of patients with acid reflux (pH<4), weakly acid reflux (pH 4–7), and healthy controls. Patient classification into the three groups was based on the results obtained from MII-pH.
A specially designed EBC sampler4 was used to collect the EBC samples from 2–5 exhalations. The EBC sample was split into two aliquots, typically about 10 µL each. In one aliquot the pH was measured with a pH-microelectrode. Total ionic concentration profile, encompassing anions, cations, and organic acids, was analysed by capillary electrophoresis in the second aliquot. Concurrently, saliva samples were acquired from the patient and healthy groups, and analysed by the Peptest lateral flow device. From all ions present in EBC and pH measurements, a few significant markers were identified. First, the pH was significantly elevated in the group with acid reflux (mean pH: 7.13; interquartile range [IQR]: 6.83–7.47; p<0.01) and in the group with weakly acid reflux (mean pH: 7.37; IQR: 7.18–7.57; p<0.01) compared to healthy controls (mean pH: 6.8; IQR: 6.65–6.99). Among the ions analysed by capillary electrophoresis, concentration of butyrate (BA) was the most significant parameter. BA was significantly elevated (p<0.01) in both the acid reflux and weakly acid reflux patient groups compared to healthy subjects; mean BA was measured at 2.29 µM, 3.33 µM, and 0.69 µM, respectively. Other ions from the EBC samples were also elevated, but the statistical significance was lower.
Pepsin was analysed in all samples with the Peptest, but its incidence could not distinguish between the groups of healthy and weakly acidic reflux patients. In the groups of patients with acid reflux, the incidence of high pepsin concentration (>75 ng/mL) was found only in 50% of the patients. We found that pH and BA concentration in EBC were the most statistically significant markers. Both can be measured easily and quickly, in <5 minutes; therefore, the initial screening for these markers can provide a fast and non-invasive check to pre-select the patients with possible GORD positivity. Unfortunately, the markers are not sensitive enough to distinguish the weakly acid and acid reflux, but can potentially be used to reduce the diagnostic cost and avoid unnecessary invasive MII-pH testing. Unlike the EBC, pepsin analysis in saliva did not provide any diagnostic value.