Incidence and Implications of Abnormal Glucose Tolerance Testing Following Gastric Bypass

Introduction: Reactive hypoglycemia following RYGB has been well reported. Its frequency and implications are unclear. To further determine its incidence and significance, glucose tolerance tests (GTT) was used to assess the effect of glucose challenge on post-RYGB patients.
Methods: 28 randomly selected patients who were at least 6 months post-op from RYGB and were returning for routine follow-up were studied. All underwent a standard GTT with measurement of corresponding insulin levels. All had anatomical studies demonstrating intact staple lines and normal post-bypass anatomy. Mean age 48.8 +/- 11.5 years, mean pre-operative BMI 48.7 +/- 6.8, mean percent excess BMI lost 65 +/- 21%. 2/3 of the patients had weight regain and the mean weight regain at follow-up was 15.3 +/- 16.9 lbs, mean follow-up time 38.4 (6-89) months.
Results: 26/28 patients had an abnormal GTT. 5/28 patients were identified as diabetic. 3 of these patients had mildly elevated fasting glucose levels and 2 patients had normal fasting glucose levels. All 5 of these patients were diabetic pre-operatively. Of the remaining patients, 91% (21/23) had evidence of reactive hypoglycemia (glucose < 60mg/dL) at 1-2hrs post glucose load. The mean 1 hr insulin level for these 23 patients was 103 +/- 96.3 µIU/mL. Within this cohort of 23 patients, 11 had a maximum to minimum glucose ratio > 3:1 with 4 having a ratio > 4:1.
Conclusions: This study demonstrates that an abnormal GTT is a common finding post-RYGB. 6 cases of diabetes were recognized among patients with normal-mildly elevated fasting glucose levels. Among patients with no prior history of diabetes, reactive hypoglycemia was found to be more common than expected. Given that insulin values were in the normal-mildly elevated range for all but 3 of those patients, these results do not support nesidioblastosis as an etiology. A large subgroup, 11/23 patients, had a profound dumping reaction with rapid elevation of glucose followed by sharp decline. We believe this is due to rapid emptying of the pouch and may contribute to maladaptive eating behaviors leading to weight regain long-term. Based on these results we have started prospective studies comparing pyloric preserving operations such as VSG and BPD-DS with non-pyloric sparing procedures such as RYGB. Finally, our data suggests that GTT is an important part of post RYGB follow –up and should be incorporated into the routine post-operative screening protocol.

Session: Podium Presentation

Program Number: S012