Receiver operating characteristic (ROC) curve to determine the diagnostic accuracy of different pH cut-offs for the fresh gastric sample versus the non-gastric samples. Receiver operating characteristic (ROC) curve to determine the diagnostic accuracy of different pH cut-offs for the fresh gastric sample versus the non-gastric samples. Anne M Rowat et al. BMJ Open Gastroenterol 2018;5:e000211 © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.