Comparison between gastric scintigraphy and the [13C]-acetate breath test with Wagner-Nelson analysis in humans

1. The [C-13]-acetate breath test (ABT) quantifies gastric emptying as the half [(CO2)-C-13]-excretion time (T-1/2b), but T-1/2b differs from the scintigraphic half-emptying time (T-1/2s). The aims of the present study were to accurately determine the half-emptying time by ABT with Wagner-Nelson analysis (T-1/2WN), to compare T-1/2WN with T-1/2s and to validate the Wagner-Nelson strategy in ABT. 2. For a comparative study, eight volunteers simultaneously underwent ABT and scintigraphy. Anterior images were acquired and breath samples were collected every 15 min for 4.0 h after ingestion of a 200 kcal liquid meal labelled with 37 MBq [Tc-99m]-colloidal sulphur and 100 mg [C-13]-acetate. For the validation experiment, another six volunteers underwent ABT, on two randomized occasions, using the 200 kcal liquid meal with 100 mg [C-13]-acetate. On either of the two occasions, a gel-forming agent was stirred into the meal to intentionally delay gastric emptying by increasing meal viscosity. Breath samples were collected at regular 15 min intervals for 4 h post ingestion. 3. The Wagner-Nelson equation for ABT is F(t) = (A(breath)(t) + C(t)/0.65)/A(breath)(infinity), where F(t) is a fractional dose of the [C-13] label emptied, C(t) is the [(CO2)-C-13] excretion (% dose/h), A(breath)(t) is the area under the C(t) curve (% dose) and A(breath)(infinity) is the ultimate [(CO2)-C-13] recovery in breath (% dose). The percentage gastric retention was estimated as 100 x (1 - F(t)). The time plots of scintigraphic activity and 100 x (1 - F(t)) were fitted to y(t) = 100 x e(-Kxt), K values were estimated mathematically for each plot by regression analysis and T-1/2s and T-1/2WN were calculated as (ln2)/K. The time versus pulmonary [(CO2)-C-13] excretion plots were fitted to z(t) = m x k x beta x e(-kt)(1 - e(-kxt))(beta-1), where m, k and beta are constants; T-1/2b was calculated as -(ln(1 - 2(-1/beta))]/k. 4. Values of T-1/2WN were closer to T-1/2s than T-1/2b, although T-1/2WN and T-1/2b yielded significant under- and overestimation of T-1/2s, respectively. The high viscosity meal significantly prolonged T-1/2WN and T-1/2b; T-1/2WN could detect the delayed transit of the viscous meal more sensitively than T-1/2b. 5. The Wagner-Nelson method improves the accuracy of the ABT.