Minimally Invasive CGM Technology (Dexcom/Abbott)

Minimally Invasive CGM Technology

Minimally invasive continuous glucose monitors (CGMs) read glucose from interstitial fluid (ISF), the fluid that bathes the cells under the skin, instead of from a drop of capillary blood. A thin sensor filament sits just below the skin and sends readings automatically. Abbott's FreeStyle Libre and Dexcom are the two companies in this article's title, but they aren't the only US options. As of October 2026, MiniMed sells the Instinct, Simplera Sync, Guardian 4 and Simplera sensors [8], and Senseonics makes Eversense 365, a sensor a clinician implants under the skin for up to a year [9]. The current Abbott and Dexcom generations are the FreeStyle Libre 3 Plus and Libre 2 Plus sensors (up to 15 days) [6] and the Dexcom G7 and G7 15 Day [3][5].

How it Works

Abbott's sensors use what the company calls Wired Enzyme technology. Glucose oxidase is cross-linked into a polymer with an osmium compound (the mediator), which carries electrons from the enzyme to the electrode at only 40 mV, low enough to avoid reacting with most interfering substances [2]. Mediators still compete with oxygen, the enzyme's natural co-substrate, for its electrons, so calling a mediated sensor "oxygen independent" overstates it [1].

Dexcom relies on flux-limiting membranes to manage the glucose-to-oxygen ratio. The underlying problem is that glucose oxidase needs oxygen as a co-substrate, so classic sensors add an outer membrane that slows glucose but lets the smaller oxygen molecule pass [1]. Here's what surprised us: the Libre sensor has a glucose-limiting membrane too, and the paper on its factory calibration calls a uniform coat of that membrane essential [2].

Accuracy is usually summarized as MARD (mean absolute relative difference), the average gap between sensor and lab readings; lower is better. In adult studies, the Dexcom G7 posted 8.2% on the arm and 9.1% on the abdomen [3], and the shared Libre 2 Plus and Libre 3 Plus sensor posted 8.2% (8.1% in ages 6 to 17) [4]. The number isn't below 10% in every group: children ages 2 to 5 came in at 11.2% [4].

Both product lines carry "non-adjunctive" FDA labeling, meaning their readings can be used for diabetes treatment decisions without a confirming fingerstick [5][6]. That idea dates to December 2016, when the FDA approved the Dexcom G5 Mobile, since discontinued, as designed to replace fingerstick testing for treatment decisions [7]. For a closer look at the electrochemistry, see our guide to CGM sensor technology mechanisms.

Impact on Traditional [Test Strips](/sell-diabetic-supplies/)

Test strips are no longer mainly a calibration tool for Abbott and Dexcom users. The Libre Plus sensors are factory-calibrated and can't be calibrated by the user [6], and the G7 15 Day is factory-calibrated with optional fingerstick calibration [5]. Eversense 365 is the exception: its labeling calls for four fingerstick calibrations at the start, one a day through day 13, then one a week [9].

Strips still matter as the backup. Both the Dexcom and Abbott labeling say to use a blood glucose meter when sensor readings don't match symptoms or expectations, and Libre readings can't be used for treatment decisions during the first 12 hours of wear [5][6]. The ADA's 2026 Standards of Care say people using CGM must have access to blood glucose monitoring at all times [11]. When to reach for the meter is a decision to make with your care team.

Physiological lag explains part of the mismatch. In healthy adults after an overnight fast, glucose took about 5 to 6 minutes to move from blood into ISF [10]. That delay matters little when glucose is steady, but when it is rising or falling fast, a sensor reports where blood glucose was a few minutes earlier.