This study summarizes pre-and post-analytical aspects of the 13C-breath-test(BT) evaluated by means of isotope selective nondispersive infrared spectrometry(NDIRS) -Isomax 4000 (Isodiagnostika). Moreover, the sources of inaccuracy in test results are identified: (a) uncertain baseline 13C abundance, (b) inaccuracy of the spectrometer, and (c) uncertainty in CO2production, which also burden cummulative BT where IR/IRMS measuring instruments are used.
Regarding (a), an estimate is presented that is closer to reality than the commonly used PDB standard. To address (b), the accuracy of measurementsis assessed by a statistical analysis and by measuring IRMS calibrated samples every four months. After 14 cycles of checking, the calculated mean bias of the Isomax 4000 equals 5.23 %. Concerning (c), two published estimates of CO2production are used and compared: a BSA-based (Body Surface Area) estimate, and a BMR-based (Basal Metabolic Rate) estimate.To measure gastrointestinal functions, 500 BT have been performed since 2002: 53 tests with 13C-xylose, 161 with 13C-mixed triglyceride, and 286 with 13C-urea. These include 215 cumulative (6 hours) 13C breath tests, especially exocrine pancreatic tests with 13C-mixed triglyceride. The cut-off value for these pancreatic tests was calculated as the mean value of the recovery levels -2SD in a group of 45 subjects without chronic pancreatitis. It is observed that the BMR-based calculation has led to greater 13C recovery values than the BSA approach. The cause of this discrepancy is explained, and a corrected, more accurate approach is proposed.
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citation: Kocna Petr, Zdislava Vaníčková, Jan Chleboun: Clinical and Laboratory Aspects of 13C-Breath Test Evaluated by NDIRS Infrared Spectrometry. Multimedia support in the education of clinical and health care disciplines :: Portal of 1-st Faculty of Medicine - Charles University [online] , [cit. 01. 10. 2020]. Available from WWW: https://portal.lf1.cuni.cz/article-468-clinical-and-laboratory-aspects-of-13c-breath-test-evaluated-by-ndirs-infrared-spectrometry. ISSN 1803-6619.