There have been many studies about the diagnosis of gastric emptying using 13C octanoic acid breath test (13C-OABT) since 1993 when Ghoos el al.(1993) first reported, and various index of 13C-OABT was investigated for the correct diagnosis. Especially, the half empting time (T1/2) calculated from fitting curve and the maximum peak time (Tmax) obtained by the actual 13C-excreation curve are used most frequently. However, some discrepancy between T1/2 and Tmax in the same subject is observed. In this report, we compared T1/2 with Tmax and discussed usefulness and problems of 13C-OABT. Subjects were 20 healthy volunteers and 55 patients with suspect of delayed gastric empting ; 50 with Diabetes Mellitus and 5 with functional dyspepsia. The subjects consumed a standard 280 kcal test meal consisting of 100 mg of 13C-octanoic acid. Breath samples were obtained before and every 15 min. after the consuming of test meal for a total of 6h. Correlation between T1/2 and Tmax was examined. As results, a significant correlation between T1/2 and Tmax was observed (γ=0.84). However, the diagnosis of T1/2 did not agree with that of Tmax in 29.7% ; 15 of 37 patients diagnosed as delayed gastric emptying by T1/2 were judged normal by Tmax. The 13C-excreation curve of these 15 patients showed delayed recovery in late phase. We speculated this delayed recovery did not result in true delayed gastric emptying but was the consequence of metabolic effect probably due to liver function. If so, the diagnosis using Tmax is considered more accurate than that using T1/2 in 13C-OABT, however requiring further study to confirm this speculation.
