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Study to determine the likely accuracy of pH testing to confirm nasogastric tube placement

Rowat, Anne M; Graham, Catriona; Dennis, Martin; Rowat, Anne


Anne M Rowat

Catriona Graham

Martin Dennis

Anne Rowat


Objective To establish the likely accuracy of pH testing to identify gastric aspirates at different pH cut-offs to confirm nasogastric tube placement.
Methods This prospective observational study included a convenience sample of adult patients who had two (one fresh and one frozen) gastric and oesophageal samples taken during gastroscopy or two bronchial and saliva samples taken during bronchoscopy. The degree of observer agreement for the pH of fresh and frozen samples was indicted by kappa (k) statistics. The sensitivities and specificities at pH ≤5.5 and the area under the receiver operating characteristics (ROC) curve at different pH cut-offs were calculated to identify gastric and non-gastric aspirates.
Results Ninety-seven patients had a gastroscopy, 106 a bronchoscopy. There was complete agreement between observers in 57/92 (62%) of the paired fresh and frozen gastric samples (k=0.496, 95% CI 0.364 to 0.627). The sensitivity of a pH ≤5.5 to correctly identify gastric samples was 68% (95% CI 57 to 77) and the specificity was 79% (95% CI 74 to 84). The overall accuracy to correctly classify samples was between 76% and 77%, regardless of whether patients were taking antacids or not. The area under the ROC curve at different pH cut-offs was 0.74.
Conclusion The diagnostic accuracy of pH ≤5.5 to differentiate gastric from non-gastric samples was low, regardless of whether patients were taking antacids or not. Due to the limited accuracy of the pH sticks and the operators’ ability to differentiate colorimetric results, there is an urgent need to identify more accurate and safer methods to confirm correct placement of nasogastric tubes.

Journal Article Type Article
Acceptance Date May 14, 2018
Online Publication Date Jun 9, 2018
Publication Date 2018-06
Deposit Date May 23, 2018
Publicly Available Date Jun 14, 2018
Journal BMJ Open Gastroenterology
Electronic ISSN 2054-4774
Publisher BMJ Publishing Group
Peer Reviewed Peer Reviewed
Volume 5
Issue 1
Article Number e000211
Keywords nasogastric tube placement, pH testing, gastric aspirates
Public URL
Contract Date Jun 14, 2018


Study to determine the likely accuracy of pH testing to confirm nasogastric tube placement (396 Kb)

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© 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.
This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:

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