Does CGM actually improve blood sugar control for people with type 1 diabetes?
Yes, and the evidence is strong. The largest and most rigorous study here — a randomized controlled trial of 156 adults with type 1 diabetes and high HbA1c — found that using an intermittently scanned CGM with optional alarms lowered HbA1c by 0.5 percentage points more than standard fingerstick testing after 24 weeks (from 8.7% to 7.9% vs. 8.5% to 8.3%) [1]. That may sound modest, but it translates to 2 hours more per day in the target glucose range and 43 minutes less time in hypoglycemia (dangerously low blood sugar) [1]. Another study in children and teens starting insulin pump therapy showed that for every extra 100 hours of CGM use per month, HbA1c dropped by 0.39% [4]. Even in a disaster scenario — after the 2023 earthquakes in Turkey — children with type 1 diabetes who had CGM access saw their HbA1c improve, while those without it got worse [6]. These are not small or trivial effects.
What are the real-world accuracy limits of CGM?
CGM is not perfectly accurate, and the hype sometimes makes it sound like it is. A careful crossover trial in 15 healthy adults found that CGM overestimated fasting glucose by an average of 0.9 mmol/L and post-meal glucose by a similar amount compared to fingerstick capillary blood tests [2]. This bias varied by the type of food eaten and from person to person — meaning CGM can misclassify the glycemic index of a food (e.g., labeling a fruit smoothie as higher-glycemic than it really is) [2]. The same study found that CGM overestimated time spent above 7.8 mmol/L by about 4-fold, and even after correcting for baseline differences, the overestimate was still 2-fold [2]. In a summer camp setting with children, the newer Dexcom G7 showed improved accuracy (mean absolute relative difference of 11.3%) compared to the older G6 (16.0%), but it still wasn't perfect [5]. So while CGM is good enough for trend-spotting and decision-making, it is not a substitute for a lab test or fingerstick when you need a precise number.
Is CGM worth it for everyone? What about the cost?
Not everyone benefits equally, and cost is a major barrier. A 24-week follow-up study of people with type 2 diabetes discharged from the hospital found that while HbA1c improved dramatically from 11.6% to 7.4% overall, only 30% of participants were still using CGM at 24 weeks — and the main reason was cost and insurance problems [3]. Among those who stopped using CGM, 75% cited financial barriers, compared to 32% of those who continued [3]. On the other hand, a cost analysis from a Russian hospital found that using CGM for patients on intravenous insulin in the ICU saved money (about $68 vs. $84 over 6 days) and saved nurses 4 hours of time per patient [7]. So for people on intensive insulin therapy — whether in the hospital or at home — CGM can be cost-effective. But for those with type 2 diabetes not on insulin, or those who have to pay out of pocket, the benefits may not justify the expense. The hype often ignores this financial reality.
About These Sources
This answer is built on 7 peer-reviewed studies — published from 2022 to 2026, 3 from 2024 or later, 1 in Q1 journals, collectively cited 161 times — selected as the most relevant from 11 studies that passed quality screening, drawn from 85 papers retrieved from a database of over 500 million.
Sources used in this answer
Intermittently Scanned Continuous Glucose Monitoring for Type 1 Diabetes
In a randomized controlled trial of 156 adults with type 1 diabetes, intermittently scanned CGM lowered HbA1c by 0.5 percentage points more than fingerstick testing and added 2 hours per day in target glucose range.
Continuous glucose monitor overestimates glycemia, with the magnitude of bias varying by postprandial test and individual - a randomized crossover trial.
In a crossover trial of 15 healthy adults, CGM overestimated fasting and post-meal glucose by about 0.9 mmol/L compared to capillary blood tests, and misclassified the glycemic index of some foods.
Benefits and Barriers to Use of CGM 24 Weeks Following Hospital Discharge
In a 24-week follow-up of 108 hospitalized patients with type 2 diabetes, HbA1c improved from 11.6% to 7.4% regardless of CGM use, but only 30% continued CGM, with cost cited by 75% of those who stopped.
Timing of CGM initiation in pediatric diabetes: The CGM TIME Trial.
In a randomized trial of 144 children with type 1 diabetes starting pump therapy, simultaneous CGM initiation led to higher adherence, and each extra 100 hours of CGM use per month was associated with a 0.39% lower HbA1c.
Benefits and Accuracy of Real-Time CGM in Children and Adolescents With Type 1 Diabetes Attending Summer Camp: Second Year.
In a camp study of 21 children with type 1 diabetes, the Dexcom G7 showed improved accuracy (mean absolute relative difference 11.3%) compared to the older G6 (16.0%), and was rated higher in usefulness.
Effect of Continuous Glucose Monitoring Device Assistance on Glycemic Control of 2023 Kahramanmaras Doublet Earthquake Survivors with Type 1 Diabetes in Adana, Turkey
In a retrospective study of 134 children with type 1 diabetes after the 2023 Turkey earthquakes, those using CGM had improved HbA1c, while those without CGM had worse control; the benefit was stronger in adolescents.
LBODP063 The Benefits Of Using Cgm For Intravenous Insulin Therapy
In a hospital study of 72 cycles of CGM use for intravenous insulin therapy, CGM saved nurses 4 hours of time over 6 days and was slightly cheaper than fingerstick testing ($68 vs. $84).