Glucose monitors for people without diabetes: the first independent test

An over-the-counter continuous glucose monitor is a coin-sized skin sensor that samples glucose in the fluid just under the skin every few minutes and streams the readings to a phone; since 2024 the US Food and Drug Administration has cleared versions sold with no prescription to anyone who does not use insulin, including people with no diabetes at all [s1]. The first independent test of how well these consumer sensors track blood sugar in people without diabetes found they follow the broad direction of a rise or fall but miss the exact number often enough to be a weak basis for a diagnosis or a real-time decision about food [s2].

That gap matters because of who is now wearing them. The devices were built to spare people with diabetes the finger-prick, and for insulin dosing their accuracy is well characterised. The new market is different: healthy adults buying a sensor for weight management, athletic training or "metabolic screening," a use the manufacturers actively encourage and the evidence has barely examined.

What the FDA actually cleared

In March 2024 the FDA cleared Dexcom's Stelo Glucose Biosensor System, the first over-the-counter continuous glucose monitor, for adults 18 and older who do not use insulin — a group the agency described as including people managing type 2 diabetes without insulin and people without diabetes who want to see how food and activity move their glucose [s1][s3]. The clearance came with an explicit caveat: the system is not for anyone with problematic hypoglycaemia, because it is not designed to warn of a dangerously low reading, and users "should not make medical decisions based on the device's output without talking to their healthcare provider" [s1]. Other manufacturers have since entered the same non-prescription category.

A clearance is a statement that a device is reasonably safe and performs as described for its intended use — not that wearing one makes a healthy person healthier. On that second question the FDA said nothing, because that was not what it reviewed.

The first independent accuracy check

Until recently the only accuracy data on these consumer sensors came from their makers. A team led from Yale ran what it describes as the first independent evaluation of over-the-counter CGM accuracy in the population now being sold the devices: 39 adults without diabetes, wearing the sensors across sessions that combined rest or exercise with either a sugar-sweetened drink or a placebo, deliberately staging the moments when someone might glance at the reading and act on it [s2].

Against a capillary fingerstick meter, the sensors' overall mean absolute relative difference — the average gap between sensor and reference, where lower is better — was 12.9%, with a mean bias of −4.8 mg/dL and readings landing within 15% or 15 mg/dL of the reference only 66.5% of the time [s2]. The error was not evenly spread. After a sugary drink, when glucose was moving fastest, disagreement rose to a MARD of 15.3%, against 10.6% after the placebo drink (P < .01); exercise had no consistent effect [s2]. Sensors also lagged the blood: applying a uniform five-minute delay improved MARD to 11.2%, and the authors estimated a population lag of about 6.2 minutes [s2]. In practical terms, 13.8% of the directional change arrows the apps display — the up, down and steady indicators a user reads at a glance — were classed as carrying a moderate-to-extreme risk of being misleading [s2].

Why the numbers are sobering, not damning

The honest reading is mixed rather than dismissive. The sensors "seemingly agreed with overall capillary glucose trends but were less reliable for exact-value agreement," the authors conclude, and "may aid lifestyle monitoring but warrant caution for diagnostic thresholds, real-time change-indicator use, and research" [s2]. For watching whether a habit nudges your glucose curve over weeks, a sensor that is roughly right on the trend is probably good enough. For the uses that get marketed hardest — reacting to a single number after a meal, or reading a spike as evidence of prediabetes — the same error is large enough to mislead, and it is worst exactly when glucose is changing quickly, which is when people look [s2]. This is a study in young adults without diabetes and it measured agreement, not whether acting on the readings improves any health outcome, which remains untested.

Why it matters

An over-the-counter CGM reaches the wearer, as the authors note, often before any structured teaching on how to read it [s2]. A false spike can send someone toward needless anxiety or an eliminated food; a reassuring flat line can do the opposite. That places these devices in the same category as the other consumer sensors this site has weighed — glucose readings from smartwatches that never touch the skin's chemistry, the general-wellness carve-out that lets a device make health-adjacent claims without proving them, and the recurring distance between a consumer gadget and a validated clinical measurement. Even in the group it was designed for — people with diabetes — continuous monitoring earns its keep through what a clinician does with the data, not the sensor alone.

What to watch

Whether independent accuracy data accumulate for the specific sensors on sale and for older, heavier and more metabolically varied users than this young cohort; and whether any trial tests the thing the marketing implies — that a person without diabetes who watches their glucose ends up healthier for it. Until then, the useful thing to know is that these are trend meters, not precision instruments, and that the reading is least trustworthy in the minute after you eat.

This article is informational and is not medical advice.

Sources

• [s1] "FDA Clears First Over-the-Counter Continuous Glucose Monitor." U.S. Food and Drug Administration, news release, 5 March 2024. https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor
• [s2] Prakash N, Barrows AH, Stults-Kolehmainen M, Loza AJ, Kilpatrick MW, Ash GI. "Agreement of Over-the-Counter Continuous Glucose Monitors With Capillary-Meter Glucose in Young Adults Without Diabetes." Journal of Diabetes Science and Technology, published online 20 September 2026. https://doi.org/10.1177/19322968261482150
• [s3] Mahase E. "FDA approves first over-the-counter blood glucose monitor for diabetes." The BMJ, 384:q611, 11 March 2024. https://doi.org/10.1136/bmj.q611