Why CGM data is suddenly a product question
Since FDA cleared the first over-the-counter CGM in March 2024 (FDA press release, Mar 5, 2024), people can buy a CGM without a prescription. Nutrition, metabolic-health and wellness products now want to use CGM data, and research teams want it as an outcome. To use it well you need to know which device type you're dealing with, which metrics are standard, how the data reaches you, and which claims would turn your product into a regulated device.
CGM types: prescription vs. over-the-counter
| Type | Who can use it | Labeled intended use (examples) | Data access | Source |
|---|---|---|---|---|
| Prescription iCGM (e.g., Dexcom G6) | Persons age 2 years and older with diabetes (G6), by prescription | Management of diabetes. Intended to replace fingerstick testing for treatment decisions, and can communicate with digitally connected devices including automated insulin dosing systems | Manufacturer app and cloud; developer API where offered (see below) | FDA De Novo DEN170088 |
| OTC iCGM: Dexcom Stelo | Adults 18+ who don't use insulin. Not for people with problematic hypoglycemia | Includes people with diabetes on oral medications, and people without diabetes who want to understand how diet and exercise affect glucose. Readings in the app every 15 min. Users shouldn't make medical decisions without talking to a provider | Smartphone app | FDA press release, Mar 5, 2024 |
| OTC iCGM: Abbott Lingo | People 18+ not on insulin | Helps detect euglycemic and dysglycemic levels, and may help users understand how lifestyle and behavior, including diet and exercise, affect glucose. Not intended for medical action without a healthcare professional | Smartphone app | FDA decision summary K233655 |
| OTC iCGM: Abbott Libre Rio | Non-insulin-using persons 18+ | Detects trends and tracks patterns. Aids detection of euglycemia, hyperglycemia and hypoglycemia. Can communicate with digitally connected devices | Per labeling: digitally connected devices | FDA clearance letter K233861 |
Examples only, from FDA documents, not endorsements. Always read the current labeling and the 510(k) or De Novo record for the exact device and version you use.
Core CGM metrics
The International Consensus on Time in Range (Battelino et al., Diabetes Care 2019) standardized how CGM data are summarized. Use these definitions so your outputs are comparable with the literature.
| Metric | Definition | Consensus target (type 1/type 2 diabetes) | Source |
|---|---|---|---|
| Data sufficiency | Days worn and % of time CGM is active | 14 days; 70% of data from 14 days | Battelino et al., Diabetes Care 2019 |
| Time in range (TIR) | % of readings 70–180 mg/dL (3.9–10.0 mmol/L) | >70% (>50% for older/high-risk) | Battelino et al., Diabetes Care 2019 |
| Time below range (TBR) | % <70 mg/dL; % <54 mg/dL | <4%; <1% | Battelino et al., Diabetes Care 2019 |
| Time above range (TAR) | % >180 mg/dL; % >250 mg/dL | <25%; <5% | Battelino et al., Diabetes Care 2019 |
| Coefficient of variation (CV) | Glycemic variability (SD ÷ mean) | ≤36% | Battelino et al., Diabetes Care 2019 |
| Glucose management indicator (GMI) | GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL) | n/a (an estimate of A1C, not a lab value) | Bergenstal et al., Diabetes Care 2018 |
The consensus targets are for people with diabetes, and separate targets apply in pregnancy. They aren't validated targets for people without diabetes, and this page isn't clinical or dosing advice.
Data access for developers
Example: the Dexcom API (from Dexcom's official developer docs). Check the current docs and terms for any vendor before you build.
- Retrospective, not real-time. Data uploaded from Dexcom mobile apps is available with a one-hour delay in the US and a three-hour delay outside the US. Dexcom says the API is meant for retrospective data, not real-time treatment decisions (Dexcom API endpoint overview; Dexcom developer FAQ).
- OAuth 2.0 and query windows. Every request needs a bearer token. Data queries take a startDate and endDate window of at most 30 days (Dexcom API endpoint overview).
- Two clocks. Records carry
systemTime(device UTC, subject to drift) anddisplayTime(what the user sees) (Dexcom API endpoint overview). Pick one on purpose for alignment with other wearables. - Out-of-range values. EGV values of 39 and 401 mean below 40 or above 400 mg/dL, the limits of the measuring range (Dexcom /egvs reference). Handle them explicitly in your metrics code.
- Rate limits. 60,000 calls per app per hour (Dexcom API endpoint overview).
Gaps and sensor changes are missing data. See wear time and missing data in wearable studies.
Wellness claim vs. device claim
Showing a user their glucose and general lifestyle information is very different from telling them what their glucose means for a disease, or what to do about it. Interpretation, diagnosis or treatment claims can make your software a medical device in its own right, even if the sensor is already cleared. Work through our is my app a medical device? guide before you write product copy.
From our research
Mike Hittle is a co-author of an NIH workshop report on precision nutrition (Lee BY, Ordovás JM, … Hittle M, … Martinez MF. "Research gaps and opportunities in precision nutrition: an NIH workshop report." Am J Clin Nutr. 2022;116(6):1877–1900. doi:10.1093/ajcn/nqac237). From the abstract: "Responses to dietary change and the resulting health outcomes from consuming different diets may vary significantly between people," and "The workshop concluded that much research will be needed before more precise nutrition recommendations can be achieved. This includes better understanding and accounting for variables such as age, sex, ethnicity, medical history, genetics, and social and environmental factors."
Related
Frequently asked questions
Do I need a prescription CGM for my study or product?
Not necessarily. FDA has cleared over-the-counter CGMs for adults 18+ who don't use insulin (FDA press release, Mar 5, 2024). Check that your population and use match the device's labeled indications.
What is time in range?
Time in range is the percentage of CGM readings between 70 and 180 mg/dL. The international consensus target for most people with type 1 or type 2 diabetes is more than 70% (Battelino et al., Diabetes Care 2019).
Can my app get real-time CGM data?
It depends on the vendor. Dexcom's developer API provides retrospective data, with a one-hour delay in the US and three hours outside the US (Dexcom developer FAQ).
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