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

Abstract It is assumed, although not proven, that ¹³CO₂‐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 CO₂‐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 T½ 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 T½ 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 = 0.028, P < 0.0001). T½_NL and 4h‐CUM were weakly correlated, even after exclusion of tests with unrealistically high estimates for T½_NL (n = 1095, R² = 0.029, P < 0.0001). Conversely, 4h‐CUM was closely associated with T½_GLR (exponential correlation, R² = 0.774, 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 ¹³CO₂‐excretion for evaluation of ¹³C‐OA‐breath tests and suggest that such models may correctly identify T½ in a mixed patient population.