Art. 1.1397

Principle of 13C-octanoic Acid Breath Test The rationale of 13C-octanoic acid breath test (13C-OBT) to measure gastric emptying of solids is based on (1) the firm retention of 13C-octanoic acid in the solid phase of a standard test meal during its passage through the gastric environment, followed by (2) a rapid disintegration of the solid phase in the duodenum with (3) subsequent absorption of 13Coctanoic acid and (4) hepatic oxidation to CO2 (Figure 1). In vitro validation studies7 have shown that in gastric environment 13Coctanoic acid is firmly retained in the yolk of scrambled egg used as test meal. Once the meal reaches the duodenal lumen, 13C-octanoic acid is rapidly absorbed through intestinal mucosa and oxidized to CO2 in liver. The appearance of CO2 in breath after oral administration of 13C-octanoic depends mainly by the gastric emptying of the egg yolk into the duodenum (rate limiting step). The other metabolic steps (absorption and oxidation) do not influence the rate of breath CO2 excretion as shown by studies7 in which, after duodenal instillation of 13C-octanoic acid, CO2 appears in breath almost immediately with a very little inter-subject variability.