Bariatric Surgery Study Shows Potential of Using CGM in Clinical Research

In 2017, as advocates and researchers discussed the potential for continuous glucose monitoring (CGM) to become a tool in clinical trials, most of the discussion involved testing in new therapies.^1,2 The discussion culminated in an international consensus on CGM, published in December 2017, that included standards for assessing hypoglycemia in clinical trials.³

From the start, the Abbott FreeStyle Libre Pro, approved in September 2016, appeared to be the default CGM choice for clinical trials: It is factory calibrated, does not require patient interaction, and allows healthcare professionals to download the glucose data after 14 days.⁴ In September 2017, the FDA approved the FreeStyle Libre Flash CGM for consumer use with a 10-day sensor; it approved the 14-day sensor in July 2018.⁵

In February, a small study published in the journal Obesity Surgery⁶ showed that CGM technology is already giving researchers the ability to not only track minute-by-minute data but also customize surgical or therapeutic interventions for individual patients.

In the study, researchers from Jagiellonian University Medical College in Krakow, Poland, used the FreeStyle Libre CGM to study patients with and without type 2 diabetes (T2D) who underwent 2 methods of bariatric surgery, laparoscopic sleeve gastrectomy and laparoscopic Roux-en-Y, also known as gastric bypass. Of the group, 16 patients had T2D and 16 did not; 18 had the sleeve procedure and 14 had gastric bypass. Patients were tracked for the 10-day postoperative period, from the day of surgery onward.

Patients in the study had a body mass index of 35 to 50 kg/m². Their diabetes was very well controlled: The median glycated hemoglobin (A1C) in the patients with T2D was 5.5%, which did not differ from that of the control group (P = .460.) Preoperative daily blood glucose concentration between the 2 groups was also similar (P = .622).

Although the mean postoperative blood glucose concentration over the length of the study was similar between the 2 types of surgical groups and between those with and without T2D, use of CGM revealed different patterns, giving physicians insights into when diabetes therapy should be altered to prevent hypoglycemia.

The research team found the following results:

• Among the 32 patients, glucose concentration was within the target range of 3.9 to 6.7 mmol/L 68% of the time during the 10-day postoperative period.
• There were 12 ± 6 low-glucose events (<3.9 mmol/L) per patient, which were more frequent among the T2D patients than those without the disease (14 ± 5 events vs 9 ± 6 events; P = .035).
• After gastric bypass, patients with T2D had more low blood glucose episodes that lasted significantly longer than patients with T2D who had the sleeve procedure (P = .035 and P = .049, respectively).
• Although mean daily glucose concentrations did not differ between the groups on days 1 to 3, by day 4, the CGM showed significantly lower CGM concentrations for patients with T2D who received gastric bypass compared with those who had the sleeve procedure; symptoms were seen in 4 patients with T2D who had gastric bypass that required glucose infusions.
• Just 2 patients did not have any hypoglycemia; both had the sleeve procedure. Low-glucose events, most occurring without symptoms, were seen in all the other patients at some point.

The authors noted that prior studies had tracked glucose status after bariatric surgery but for shorter periods; this pilot study was one of the first to use CGM to compare 2 surgical methods and follow patients for 10 days. The CGM showed that patients both with and without T2D had rapid rise in interstitial glucose concentration right after surgery, with a higher increase seen in those who had the sleeve procedure, although the difference was not statistically significant. This was consistent with prior study findings showing hyperglycemia immediately after surgery, which can result in complications and hospitalization.

The study’s chief finding—pinpointing the drop in blood glucose levels after the third postoperative day for patients with T2D undergoing gastric bypass&mdash;is likely explained by greater incretin release following the procedures, the authors concluded. “This finding, if replicated in a larger-scale, longer-term study, preferably a randomized controlled trial, would indicate a need for an early reduction in the dose of [T2D] medication,” they wrote. Thus, they concluded, for these patients, therapy should be cut back even before weight loss begins.

Forthcoming studies will make use of the FreeStyle Libre Pro. Joslin Diabetes Center is leading a study that examines the relationship between blood glucose levels and retinopathy and nephropathy risk; participants who use the CGM are asked to mail the sensor to the coordinating center after wearing it for 14 days. Data collection is expected to be finished June 30, 2019.⁷ REFERENCES:

1. Caffrey M. “Beyond A1C” pinpoints metrics that matter to patients for future FDA approvals. The American Journal of Managed Care^® website. ajmc.com/newsroom/beyond-a1c-pinpoints-metrics-that-matter-to-patients-for-future-fda-approvals. Published July 21, 2017. Accessed February 14, 2019.
2. Schnell O, Barnard K, Bergenstall R, et al. Role of continuous glucose monitoring in clinical trials: recommendations on reporting. Diabetes Technol Thera. 2017;19(7):391-399. doi: 10.1089/dia.2017.0054.
3. Danne T, Nimri R, Battelino T, et al. International consensus on use of continuous glucose monitoring. Diabetes Care. 2017;40(12):1631-1640. doi: 10.2337/dc17-1600.
4. Abbott receives FDA approval for the FreeStyle Libre Pro System, a revolutionary diabetes sensing technology for healthcare professionals to use with their patients [press release]. Abbott Park, IL: Abbott; September 28, 2016. abbott.mediaroom.com/2016-09-28-Abbott-Receives-FDA-Approval-for-the-FreeStyle-Libre-Pro-System-a-Revolutionary-Diabetes-Sensing-Technology-for-Healthcare-Professionals-to-Use-with-Their-Patients. Accessed February 26, 2019.
5. Abbott’s FreeStyle Libre 14 Day Flash glucose monitoring system now approved in U.S. [press release]. Abbott Park, IL: Abbott; July 27, 2018. prnewswire.com/news-releases/abbotts-freestyle-libre-14-day-flash-glucose-monitoring-system-now-approved-in-us-300687894.html. Accessed February 26, 2019.
6. Wysocki M, Szopa M, Stefura T, et al. Continuous glucose monitoring in bariatric patients undergoing laparoscopic sleeve gastrectomy and laparoscopic Roux-en-Y gastric bypass [published online February 8, 2019]. Obes Surg. doi: 10.1007/s11695-018-03684-5.
7. PERL Continuous Glucose Monitoring (CGM) Study. clinicaltrials.gov/ct2/show/NCT03334318. Updated November 8, 2017. Accessed February 14, 2019.

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