Are CGMs Really Safe for Dosing?


If you’ve been looking to safely ditch pricking your finger 10 times a day in order to confirm your blood glucose levels, well, your time may have come.

Just months after the FDA approved the first exclusive use of a continuous glucose monitor (CGM) system for blood glucose monitoring, a major diabetes care study has confirmed using a stand-alone CGM system to make insulin-dosing decisions is as safe and as effective as using the traditional two-fold approach of reading levels with a CGM and then confirming them with a blood glucose meter (BGM) finger-stick test.

The study, the results of which were released in February, was conducted by T1D Exchange, a Boston-based nonprofit that specializes in T1D care and research. Tidepool provided the diabetes data platform that study participants used to gather data at home and in clinic. The Jaeb Center for Health Research, the coordinating center for the study, wrote software that analyzed study data in real time using Tidepool’s APIs.

Over six months, 226 type 1 diabetes (T1D) patients at 14 diabetes care clinics were split into two groups. One group dosed their insulin based on a CGM reading alone, while the other group used BGM finger-stick measurements to confirm their CGM reading before taking insulin.

Over the study period, the CGM-only group reported a baseline HbA1c of 7.1 percent, while the CGM and BGM group reported a 7 percent baseline. Furthermore, no additional risks or complications were reported in the CGM-only group.

“This study is an important step to support regulatory pathways for the automation of insulin delivery for people with type 1 diabetes,” says Dana Ball, the executive director and co-founder of T1D Exchange. “These data are supportive of the recent FDA decision to approve the Dexcom G5 indication for insulin dosing.”

It’s important to note that the study was limited to healthy adults. Participants had to be 18 or older, diagnosed with T1D for one year or longer, treated with an insulin pump for at least three months, and be without a severe hypoglycemic event for at least one year.

On The Heels of FDA-approval

In December, the U.S. Food and Drug Administration approved sole use of Dexcom’s G5 Mobile Continuous Glucose Monitoring System for blood-sugar monitoring and insulin-dosing decisions in T1D patients two years old or older. CGM systems were previously approved to complement, not replace, finger-stick testing for diabetes treatment decisions.

Caregivers believe the combination of FDA approval and the first post-approval clinical trials by T1D Exchange may open up new paths towards convenient and less-invasive treatment for T1D patients.

“As a practicing endocrinologist, I typically advise my patients who use CGM technology to make treatment decisions based on a BGM reading,” said Dr. Grazia Aleppo, lead author of the study. “However, many of my patients often use CGM readings to make decisions about insulin doses. The results of this study assures clinicians that patients using CGM for treatment decisions is as safe and effective as BGM.”

Gaining Popularity

The results of the study come a crucial time as CGM use is on a serious rise in the U.S.

For years, T1D diabetes patients have relied on blood glucose monitoring finger-stick tests to measure their blood glucose level (BGL) and make insulin-dosing decisions. The process, while accurate and safe, is labor-intense and painful. On the other hand, CGM systems consist of small monitors that automatically capture real-time blood sugar levels via a sensor inserted under the skin.

According to T1D Exchange’s Clinic Registry, which tracks care data on 32,000 T1D patients, CGM use tripled between 2002 and 2015, with 21 percent of patients now using a CGM system.

One significant benefit of the study is the confirmation of safety. While doctors have advised patients against relying on CGM systems alone, it appears patients haven’t been listening all that well. The study reported that historically only 29 percent of CGM users confirmed their blood sugar levels with a BGM test before taking insulin. On the other hand, 44 percent of participants relied solely on their CGM system readings before deciding whether to take insulin. It appears that 44 percent, and others like them, can continue their practice without medical risk or guilt over ducking their doctor’s advice.

Insurance Impact

While most private insurance companies have covered or partially covered CGM devices for a while now, coverage of the devices has been consistently denied to Medicare beneficiaries.

That all changed after the FDA approval. In January, the U.S. Centers for Medicare and Medicaid Services ruled that FDA-approved CGM systems would now be included in a benefit category, making them reimbursable by Medicare.

While implementation process is underway, Medicare will not pay for your device today. A huge hurdle, however, in diabetes care has been cleared, at least opening the door to coverage for the first time ever.

The hope is that more clinical studies like the T1D Exchange trials will provide enough data to gain FDA-approval and total insurability for other CGM systems on the market.

Read FDA Approves Dexcom G6.

WRITTEN BY Greg Brown, POSTED 04/07/17, UPDATED 10/08/22

Greg Brown is a freelance health, finance and environmental writer living in the mountains of western Maine. He has written for Consumer Reports Magazine, Consumer Reports Online, The New York Times and The Chicago Tribune, among other publications. He holds an MFA in Fiction Writing from the University of Iowa Writers' Workshop and an MS in Journalism from Columbia University. He can be reached at