Accuracy of biochemical markers for predicting nasogastric tube placement in adults - a systematic review of diagnostic studies
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 <0.90). Conclusions Due to the heterogeneity of the studies and small sample sizes, conclusions about the diagnostic performance of the different tests cannot be drawn. Better designed studies exploring the accuracy of diagnostic tests are needed to improve the diagnostic policy. Until stronger evidence becomes available practice related to the diagnostic tests used within the clinical setting will continue to be dictated by local preferences and cost factors.