Continuous glucose monitors (CGMs) have gained popularity among individuals without diabetes for various purposes, including lifestyle modification and metabolic screening. This study, published in the Journal of Diabetes Science and Technology, investigates the agreement of over-the-counter continuous glucose monitors (OTC CGMs) with capillary glucose measurements in young adults.
What this study does not show
While the study provides insights into the accuracy of OTC CGMs, it does not establish their reliability for diagnosing diabetes or making critical health decisions based on exact glucose values.
Evidence scorecard
- Analytic validity: Established – The study evaluated the performance of OTC CGMs against a standard capillary meter.
- Clinical validity: Partial – The study assessed agreement but did not measure health outcomes based on CGM data.
- Clinical utility: Not established – The study did not demonstrate that acting on CGM results led to improved health outcomes.
The evidence class for this study is primary_research, and it involves human participants without diabetes.
The study involved 39 participants who wore OTC CGMs during different conditions, including rest and exercise, while consuming either a placebo or a sugar-sweetened drink. The researchers aimed to assess the agreement between CGM readings and capillary glucose measurements under these varied conditions.
Results indicated that the overall mean absolute relative difference (MARD) between the CGMs and capillary measurements was 12.9%, with a mean bias of -4.8 mg/dL. The agreement was notably lower when participants consumed sugar-sweetened drinks compared to placebo, suggesting that carbohydrate intake can affect CGM accuracy. Specifically, the MARD was 15.3% during sugar consumption versus 10.6% during placebo consumption.
Interestingly, exercise did not show a consistent impact on CGM performance. However, the study found that disagreement between CGM readings and capillary measurements increased with faster rates of glucose change and, to a lesser extent, at higher glucose levels. A uniform 5-minute delay in CGM readings improved the MARD to 11.2%, indicating that timing may play a role in the accuracy of these devices.
Furthermore, the study noted significant interparticipant variability in CGM performance, which could not be attributed to measured biological variables. This suggests that individual differences may influence how accurately a CGM reflects glucose levels. Notably, 13.8% of the directional arrows indicating changes in glucose levels were classified as moderate to extreme risk, highlighting potential concerns regarding the reliability of real-time change indicators.
In conclusion, while OTC CGMs appear to provide a reasonable agreement with capillary glucose trends, they are less reliable for precise value agreement, particularly after carbohydrate intake and during rapid glucose changes. Clinicians may guide patients in using these monitors for lifestyle tracking but should caution against using them for critical health decisions, such as diagnosing hypoglycemia or diabetes, which require confirmatory testing.