CGM vs Flash Monitoring in Diabetes With Hypoglycemia Unawareness

Liam Davenport

March 16, 2017

MANCHESTER, UK — Real-time continuous glucose monitoring (CGM) significantly reduces the amount of time spent in hypoglycemia and improves hypoglycemia awareness compared with intermittent 'flash' glucose monitoring in type 1 diabetes patients with impaired hypoglycemia awareness, say UK researchers.

The study, which was sponsored by the manufacturer of the CGM device, the G5 by Dexcom, nevetheless showed that both CGM and intermittent flash glucose monitoring (using Abbott's Freestyle Libre) significantly improved HbA1c levels and the amount of time spent in the target glucose range, Monika Reddy, MD, division of diabetes, Imperial College, London, UK, told the Diabetes UK Professional Conference 2017 last week.

Dr Reddy said that "real-time CGM has a greater beneficial impact on hypoglycemia outcomes and hypoglycemia awareness than intermittent flash glucose monitoring" in this admittedly high-risk population — those with impaired hypoglycemia awareness — adding that real-time CGM also "significantly reduces hypoglycemia fear" over flash monitoring.

"These findings are important when selecting monitoring technologies to minimize the clinical, and cost, impact of hypoglycemia," she noted.

But session chair Dev Singh, MD, a consultant in diabetes and endocrinology at Royal Wolverhampton NHS Trust, UK, told Medscape he wasn't convinced that this head-to-head comparison between two fairly different types of glucose monitoring technologies reflects real-world clinical use.

Comparing Apples and Oranges

The FreeStyle Libre system was licensed in Europe in 2014, and a professional version for use by physicians has been approved by the US FDA while the consumer version awaits approval there. As reported by Medscape, real-world data from more than 50,000 users indicates that the FreeStyle Libre improves glycemic control in people with diabetes, most of whom had type 1 diabetes.

Meanwhile the Dexcom G5 system was first approved by the FDA in 2016 and was later granted an additional indication when it became the first CGM system licensed to replace finger-stick testing for determining insulin doses, based on the results of the REPLACE-BG study, which showed it is safe and effective in adults with well-controlled type 1 diabetes at low risk for severe hypoglycemia.

Approached for comment after Dr Reddy's presentation, Dr Singh described her research as "nice," but said that directly comparing the two technologies does not reflect the real world, as "clinicians wouldn't work that way."

"In my mind, something like flash blood glucose testing is a step up from what they [patients] might be doing, but isn't the high-tech CGM. It's cheaper, it's more convenient, and it might solve the person's problem," he told Medscape Medical News.

The FreeStyle Libre system consists of a glucose sensor inserted into the back of the upper arm for up to 14 days and a scanner that users wave over the sensor to obtain readings. Like conventional CGM, it measures interstitial fluid glucose levels in real time.

However, it offers the advantages of longer sensor wear, no requirement for calibration, and lower cost. On the other hand, it doesn't have an alarm for low and high glucose values, and so has been described as "very different" from CGMs.

Dr Singh noted: "What would bubble up would be the people [for whom FreeStyle Libre] didn't solve the problem . . . who would then go to CGM. In clinical practice, I would apply it in different sorts of patients with different tiers of problems. So when you compare them head-to-head, you might get funny answers."

Describing the choice over the technologies as "horses for courses," he continued, "They require absolutely different processes. One machine is telling you what to do, and the other one is asking you to work out what to do."

"If something is cheaper and more convenient, I would use that [first] . . . and if it doesn't solve the problem, you move on."

Impaired Hypoglycemia Awareness Affects Up To a Third With Type 1 Diabetes

Up to one-third of adults with type 1 diabetes have impaired hypoglycemia awareness, placing them at increased risk of severe hypoglycemia and mortality. In the UK, CGM is generally only covered on the National Health Service for those with specific criteria, which includes impaired hypoglycemia awareness.

Dr Reddy's study involved 40 CGM-naive adults with type 1 diabetes and impaired hypoglycemia awareness. In the prospective, parallel-group investigation, patients were randomized to 'flash' monitoring or CGM after a 2-week run-in.

There were no significant differences in baseline characteristics between the two groups; around 60% of participants were men, the average age was around 50 years, and mean duration of diabetes was in the ballpark of 30 years.

The researchers found that CGM was associated with a significant reduction in the primary outcome, percentage time spent in hypoglycemia (< 3.3 mmol/L or 60 mg/dL), from baseline to 8 weeks compared with a nonsignificant slight increase with the FreeStyle Libre.

Glucose Outcomes and Gold Score

  G5 Freestlye Libre G5 vs Freestyle Libre
Outcome Baseline Final Change Baseline Final Change Change
% time in hypoglycemia* 7.7 3.5 –4.0 .004 7.0 7.8 +0.8 0.433 –4.8 .004
% time 3.9–10.0 mmol/L** 53.6 63.4 +9.7 .007 54.8 60.9 +6.1 0.001 +3.6 .307
HbA1c, mmol/mol (%) 58.6 (7.5) 55.1 (7.2) –3.5 .039 57.2 (7.4) 53.8 (7.1) –3.5 0.021 0.0 .99
Gold score 5.0 4.2 –0.8 .046 4.6 4.7 +0.1 0.609 –0.9 .09
*< 3.3 mmol/60 mg/dL.
**70–180 mg/dL.


But both groups had a significant increase in the time patients spent in the target glucose range, and there were also similar, significant reductions in HbA1c between baseline and 8-week follow-up in both groups.

But patients assigned to CGM experienced a significant reduction in the mean Gold score of impaired hypoglycemia awareness, whereas there was no significant difference in the score for users of flash glucose monitoring.

And in terms of fear of hypoglycemia, measured using the Hypoglycemia Fear Survey-II (HFS-II), patients in the CGM group experienced a reduction in total score, from 59.2 to 50.5 (P = .01), which was driven by a significant reduction in Worry section scores. There was no significant difference in HFS-II scores between baseline and final follow-up in the flash monitoring group.

Dr Reddy noted the strengths of the study are that it "explores critically important hypoglycemia outcomes in a well-defined, high-risk population" and its randomized, parallel-group design.

However, she acknowledged that the findings "may not be applicable to other [patient] populations" and that the follow-up was short.

This was an investigator-initiated study funded by Dexcom. Dr Reddy has previously received funding support for conference attendance from Medtronic, Dexcom, and Roche.

Diabetes UK Professional Conference 2017. March 10, 2017; Manchester, UK. Abstract

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