Influence of clinical parameters on the results of ¹³C-octanoic acid breath tests: Examination of different mathematical models in a large patient cohort

It is assumed, although not proven, that ¹³CO ₂-excretion following ingestion of ¹³C-octanoic acid (¹³C-OA) does not only depend on gastric emptying (GE) but also on absorption and metabolism of ¹³C-OA and endogenous CO ₂-production. Our aims were (i) to test the effects of patient characteristics and of diseases that may impair ¹³C-OA-metabolism on GE parameters. (ii) To compare different GE endpoints. Therefore, we investigated effects of age, gender, BMI and diseases with potential impact on ¹³C-OA-metabolism (including pancreatic, liver and lung disease, diabetes, IBD) on cumulative 4h-¹³CO₂-excretion (4h-CUM) and T calculated by non-linear regression model (NL, determined by shape of breath test curve) and generalized linear regression model (GLR, reflects absolute ¹³CO₂-excretion) in 1279 patients and 19 healthy controls who underwent a standardized ¹³C-OA-breath test. Digestive and metabolic disturbances hardly influenced 4h-CUM or T calculated by NL or GLR models. In the multivariate linear regression models, 4h-CUM was significantly predicted by diabetes adjusted for age, gender and IBD but influence of these parameters was small (R²=¹0.028, P < 0.0001). T _NL and 4h-CUM were weakly correlated, even after exclusion of tests with unrealistically high estimates for T_NL (n = 1095, R ²=¹0.029, P < 0.0001). Conversely, 4h-CUM was closely associated with T_GLR (exponential correlation, R²= ¹0.774, P < 0.00001, n = 1279). We conclude that influences of digestive and metabolic disturbances on ¹³CO₂-excretion following ¹³C-OA-application are generally low. Thus, our findings resolve an important criticism of methods using absolute ¹³CO ₂-excretion for evaluation of ¹³C-OA-breath tests and suggest that such models may correctly identify T in a mixed patient population.