High-Throughput Breath Volatile Organic Compound Analysis Using Thermal Desorption Proton Transfer Reaction Time-of-Flight Mass Spectrometry.

Breath analysis is highly acceptable to patients and health care professionals, but its implementation in clinical practice remains challenging. Clinical trials and routine practice require a robust system for collection, storage, and processing of large numbers of samples. This work describes a platform based upon the hyphenation of thermal desorption (TD) with proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), coupled by means of an original modification of the TD interface. The performance of TD-PTR-ToF-MS was tested against seven oxygenated volatile organic compounds (VOCs), belonging to three chemical classes (i.e., fatty acids, aldehydes, and phenols), previously identified as possible biomarkers of colorectal and esophago-gastric adenocarcinoma. Limits of detection and quantification were on the order of 0.2-0.9 and 0.3-1.5 parts per billion by volume (ppbV), respectively. Analytical recoveries from TD tubes were 80% or higher, linear response was in the low- to mid-ppbV range ( R2 = 0.98-0.99), and coefficients of variation were within 20% of mean values. The usability of the platform was evaluated in the analysis of a set of breath samples of clinical origin, allowing for a throughput of nearly 100 TD tubes for 24 h of continuous operation. All of these characteristics enhance the implementation of TD-PTR-ToF-MS for large-scale clinical studies.

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. 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.