The effects of changing temperature correction factors on measures of acidity calculated from gastric and oesophageal pH recordings

Background Recently, Medtronic notified customers that new correction factors should be used for their Slimline and Zinetics24 single-use, internal-standard pH catheters. Aim and Methods We selected 24-h recordings of oesophageal and gastric pH with the Zinetics24 from our archives for five healthy subjects and for five gastro-oesophageal reflux disease subjects who were studied at baseline and again after 8 days of treatment with a proton-pump inhibitor. All pH values obtained with the old correction factors were rescaled using the new correction factors. Values for median pH, integrated acidity and time pH <= 4 were then calculated from pH values with old and new correction factors. Results The new correction factors changed values for median pH, integrated acidity and time pH <= 4. Values for median pH and integrated acidity changed in a predictable, proportionate way, whereas values for time pH <= 4 did not. Conclusions The new correction factors will not change the interpretation of previously published results with median pH or integrated acidity. In contrast, values for time <= 4 cannot be converted in an obvious way with the new correction factors. Instead, the raw pH data will need to be rescaled and values for time pH <= 4 recalculated using the rescaled pH data.