Gastric half emptying time (T-1/2) for 4-h gastric emptying scintigraphy simplifies reporting but reduces detection of gastroparesis

Background Gastric emptying scintigraphy (GES) reports percent retention at 1, 2, and 4 h. Time to empty half the meal (T-1/2) could simplify GE reporting. Aims To compare the performance of GES T-1/2 to 1-, 2-, and 4-h retention. Methods GES studies were reviewed; results determined according to retention at 1, 2, and 4 h. T-1/2 was determined using 3 methods: (1) GES curve fitting using 0, 0.5, 1, 2, 3, and 4 h data; (2) linear interpolation using 0, 0.5, 1, 2, 3, and 4 h data; and (3) linear interpolation using only 0, 1, 2, and 4 h data. Results Of 495 patients, 265 had normal GE, 4 rapid GE (<30% retention at 1 h), and 226 delayed GE: 17 delayed only at 2 h (>60% ret); 94 delayed only at 4 h (>10% ret); and 115 delayed at both 2 h and 4 h. Strong correlations were seen between each T-1/2 method and 1, 2, 3, and 4 h %-empty values: curve-fit T-1/2 (r = -0.851, -0.942, -0.864, -0.744), linear T-1/2 using all imaging times (r = -0.848, -0.972, -0.878, -0.763), and linear T-1/2 using standard imaging times (r = -0.853, -0.974, -0.868, -0.760). The 132 min cutoff for delayed GE captures 99.1% to 100% of delayed GE at both 2 h and 4 h, 76.5% to 94.1% delayed at 2 h only, but only 36.7% to 39.4% delayed at 4 h only; 3.5 to 11.3% of patients with normal GE miscategorized as delayed. Conclusions GES T-1/2 correlates more strongly with retention at 2 h than at 4 h. T-1/2 alone may misclassify patients, particularly those with late-phase (4 h only) delays, reducing its utility for diagnosing gastroparesis.