Objective: The objective of this study was to investigate the diagnostic performance of
biochemical tests used to determine placement of nasogastric (NG) tubes after insertion in
adults.
Design: A systematic review of diagnostic studies was undertaken.
Data sources: A literature search of the bibliographic databases and the World Wide Web
was performed to locate original diagnostic studies in English or Chinese on biochemical
markers for detecting NG tube location.
Review methods: Studies in which one or more different tests were evaluated with a
reference standard, and diagnostic values were reported or could be calculated were
included. Two reviewers independently checked all abstracts and full text studies for
inclusion criteria. Included studies were assessed for their quality using the QUADAS tool.
Study features and diagnostic values were extracted from the included studies.
Results: Of the 10 studies included in this review, seven investigated the diagnostic
accuracy of pH, one investigated the diagnostic accuracy of pH and bilirubin respectively,
two a combination of pH and bilirubin and one a combination of pH, pepsin and trypsin
levels in identifying NG tube location. All studies used X-rays as the reference standard for
comparison. Pooled results demonstrated that a pH of 4.0 had the ability to predict only
63% of the tubes located in the stomach. However, a pH value of 5.5 to determine gastric
placement demonstrated a sensitivity of 0.89 (95% CI 0.82–0.94) and a specificity of 0.87
(95% CI 0.81–0.93). Bilirubin coupled with pH had a high specificity (0.99) which
demonstrated the ability of the test to identify misplaced tubes in intestine. However, the
ability of the test to correctly identify gastric placement of feeding tubes was relatively low
(sensitivity