Why non-diabetics using CGM may not be a good idea
The study compared CGM to regular fingerprick testing on blood glucose readings after consuming commercial or home-made smoothies or a glucose drink as a control.
There has been a major increase in health-conscious people seeking to use continuous glucose monitor (CGM) devices to see how diet and exercise can affect their blood sugar levels – but new research suggests that may not be a good idea.
A new randomised clinical trial – carried out by researchers at the University of Bath in the UK – found that a CGM sold by Abbott (the Freestyle Libre 2) "systemically overestimated" glucose in healthy people without prediabetes or diabetes when compared to a regular fingerprick test.
The finding is significant because people can use CGM data to make dietary and lifestyle changes, which may be unnecessary, and the erroneously high readings (indicating glycaemia) could lead them to believe they are prediabetic when they are not.
The study compared the CGM with fingerprick testing in 21 subjects – 15 women and six men – who consumed a range of carbohydrate-rich smoothies, either commercial or homemade, or a control drink containing 50g glucose. Blood glucose levels were measured every 15 minutes for two hours after the test drink.
The researchers, led by Professor Javier Gonzalez of Bath University's health department, say they found wide variations between individuals on the accuracy of the CGM on fasting blood glucose readings, and correcting for those "reduces, but does not eliminate, postprandial overestimate of glycaemia by CGM." Their study is published in the American Journal of Clinical Nutrition.
Last year, the first CGM for over-the-counter (OTC) use was approved by the US FDA, Dexcom's Stelo device, freeing up access to the technology for non-diabetic individuals who want to monitor their blood glucose levels – even though the company is targeting patients with type 2 diabetes with its product marketing. Meanwhile, Abbott launched a wearable consumer CGM under the Lingo brand last year in the UK, along with a coaching app.
The approval of these devices has already prompted a debate about the risks and benefits of using CGM in people without diabetes, given that many companies are now encouraging people to use CGM to guide lifestyle choices, with a target of maintaining blood glucose in a specific range.
"CGMs are fantastic tools for people with diabetes because even if a measurement isn't perfectly accurate, it's still better than not having a measurement at all," said Prof Gonzalez.
"However, for someone with good glucose control they can be misleading based on their current performance [and] relying on CGMs could lead to unnecessary food restrictions or poor dietary choices."
Commenting on the study, Dr Adam Collins, associate professor of nutrition at the University of Surrey, said it is highly relevant and informative, given the increasing use of CGMS by healthy, non-diabetic individuals.
"By design, CGMs sample interstitial fluid, which we assume is directly reflective of blood glucose, but yet could be influenced by other factors that impact glucose movement into tissues," he suggested.
"There will inevitably be some time lag between blood glucose and interstitial fluid changes [and] this lag could be as short as a few minutes or as long as half an hour," he added. "Such a lag can be problematic when detecting rapid changes in blood glucose."
