Experience with a simplified, standardized 4-hour gastric-emptying protocol

Gastric-emptying studies have no accepted standard methodology or reference values. A simplified standardized protocol with a large reference database has been proposed, with imaging obtained at only 0, 1, 2, and 4 h. The rationale for its 4-h length is data suggesting that delayed emptying is detected with higher sensitivity at 4 h than at 2 h. The purpose of the current investigation was to review our 2-y experience using this protocol, to determine the added value of 4-h imaging, and to determine whether the lag phase can predict delayed emptying.

After ingesting a sandwich made with (99m)Tc-sulfur colloid egg substitute, 175 patients were imaged immediately, every 10 min for 1 h, and then at 2, 3, and 4 h. Percentage retention was calculated for each interval. Sensitivities, specificities, predictive values, and receiver operating characteristic (ROC) curves were computed for the 1-, 2-, and 3-h intervals on the basis of normal 4-h values. Data were analyzed to determine the added value of the 4-h study. Thresholds were sought that optimized accuracy. ROC analysis was used to determine the predictive value of the lag phase.

Gastric emptying was delayed in 20% of patients at 2 h and in 26% at 4 h, a 29% increase in abnormal studies (P < 0.02). Of those normal at 2 h, 13% became abnormal at 4 h. Of those with delayed emptying at 2 h, 24% normalized at 4 h. Compared with the study at 4 h, the study at 2 h had a 59% sensitivity, 94% specificity, 76% PPV, and 87% NPV. ROC analysis showed that the areas under the ROC curve (AUC) were 0.75, 0.93, and 0.97 at 1, 2, and 3 h, respectively. The threshold for optimal accuracy for 3-h data was estimated to be greater than 30% retention. The accuracy of this threshold was 91%. The lag phase AUC for predicting delayed emptying at 4 h was 0.60.

This first investigation of a large referral patient population using a standardized protocol found that abnormal emptying is detected with greater sensitivity at 4 h than at 2 h and that the lag phase is not predictive of delayed emptying.