Experience with a standardized 4 hr gastric emptying protocol: Importance of the 4 hr value

Objectives Previously, our solid gastric emptying protocol (SGE) extended to 2 hrs. Recently a simplified standardized protocol with a large reference database, has been proposed with imaging at 0, 1, 2 and 4 hrs, and was adopted 2 years ago by our institution. The rationale for its 4 hr length is data suggesting that delayed emptying is detected with higher sensitivity at 4h than 2 hr. Our objective was to review our experience with this protocol and to determine the added value of the 4 hr imaging.

Methods 72 patients who underwent SGE were reviewed. Concordance rates between the 2 and 4 hr values were evaluated. Sensitivity and specificity were computed for the 2 hr interval on the basis of normal 4 hr values.

Results 47 patients were normal at both times and 9 were abnormal at both. 10 pts were abnormal at 4 hrs but normal at 2hr , and 6 pts were abnormal at 2 hr but abnormal at 4hrs for a total discordance rate of 16/72 or 22%. If the acquisition had stopped at 2 hrs, 10 pts( 14%) would have been misclassified as normal and 6 ( 8%) would have been misclassified as abnormal. Using the 240 min classification as the gold standard, the 120 min test was found to have a sensitivity of 0.47 (95%CI: 0.25 to 0.71) and a specificity of 0.88 (CI:0.76 to 0.95). Again using the 4hr measure as a gold standard a ROC curve was obtained. The ROC curve suggests that in our data the 120 min cutoff at 40% emptying may not be optimal; a higher accuracy and a lower false negative rate can be achieved using a 60% cutoff; Higher accuracy (83%) was obtained at a 120 min cutoff of 60% where sensitivity was 0.84 (CI:0.59-0.95) and specificity was 0.83 (CI:0.69-0.91). At this cutoff there were only 3 false negatives (44 true neg, 9 false positives and 16 true positives).

Conclusions Our results confirm the necessity of obtaining the 4 hr value for more accurate results. However if overriding considerations require a shorter acquisition, the adoption of a higher (60%) cutoff for the 2 hr emptying value may accomplish the same goal