Development and validation of a lipase nasogastric tube position test

BACKGROUND: Nasogastric tube position should be checked every day by either aspirate pH or chest radiography to prevent fatal misplaced feeding into the lungs. Many patients do not have acidic gastric aspirates and require daily chest radiographs. We developed and validated a lipase test that was compatible with non-acidic gastric aspirates. METHODS: We conducted evaluations of diagnostic test accuracy at a teaching hospital in development and validation stages. Development: We collected gastric and lung aspirates from 34 consecutive patients. We measured pH and human gastric lipase activity in the laboratory. These data helped us develop the lipase test. Ingenza Ltd (Roslin, Scotland) created tributyrin-coated pH test paper, which human gastric lipase converted into butyric acid, thus correcting false negatives. Validation: We tested nasogastric feeding tube aspirates from 36 consecutive patients with pH and lipase tests, using chest radiography or trial by use as the reference standard. RESULTS: Development: We demonstrated human gastric lipase activity in the non-acidic stomach aspirates. Validation: The accuracy of the lipase test (sensitivity 97.2%, specificity 100%) was significantly better than pH (sensitivity 65.7%, specificity 100%, p<0.05). CONCLUSIONS: When nasogastric tube stomach aspirates were not acidic and pH was falsely negative, the lipase test showed a true positive and was significantly more accurate.