ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2017) 48 OC1 | DOI: 10.1530/endoabs.48.OC1

Which test should the bariatric physician use to test for postprandial hypoglycaemia - prolonged oral glucose tolerance test versus mixed meal test?

George Tharakan1, Preeshila Behary1, Werd Al-Najim1, Harvinder Chahal1, Alexander Miras1, Ahmed Ahmed2, Stephen Bloom1 & Tricia Tan1

1Imperial College London, London, UK; 2Imperial College Healthcare NHS Trust, London, UK.

Background: An increasingly recognized complication of Roux-en-Y Gastric Bypass (RYGB) surgery is the development of postprandial hypoglycaemia (PPH). However, there remains no agreed standard on how to diagnose this condition. Commonly used tests include a prolonged oral glucose tolerance test (POGTT) and mixed meal tolerance test (MMTT). Little is known regarding how these tests compare in the post-bariatric population.

Methods: Ten patients who had confirmed PPH on CGMS underwent both a POGTT and MMTT on two different days, separated by 1 week. For both tests, volunteers attended fasted, and had regular venous sampling for glucose, insulin, GLP-1, GIP and glucagon. For the MMTT, Ensure Plus (13.8 g of protein, 10.8 g of fat, 44.4 g of carbohydrates, 330 kcal, 220 ml, Abbott, Maidenhead, UK) was used. For the POGTT, 75 g of anhydrous glucose was used.

Results: Seven of the 10 patients had biochemical hypoglycaemia during the POGTT (70% sensitivity) compared to only two during the MMTT (20% sensitivity). Consistent with this, there was a significantly lower glucose nadir during the POGTT (Mean ± S.E.M.; glucose nadir 3.64±0.27 in POGTT versus 2.68±0.18 in MMTT (P<0.0002)). Counterintuitively, although the peak insulin response was higher in during the POGTT, there was a significantly higher peak incretin response (both GLP-1 and GIP) during the MMTT. Whilst there was a trend for glucagon to decrease during the POGTT, in the MMTT, there was a rise prior to the glucose nadir.

Discussion: This comparison of two commonly used provocation tests for PPH demonstrated that the POGTT was more sensitive at detecting hypoglycemia. However, the POGTT can be considered less physiological than the MMTT as it contains only one carbohydrate. The protein and fat contained in the MMTT more closely reflects a normal meal and this may account for the differences in both incretin response as well as postprandial glucagon concentration.

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