CGM Accuracy Concerns for Critically Ill Hospital Patients

What Was Studied and Why It Matters

Continuous glucose monitors (CGMs) — the wearable sensors that track blood sugar around the clock — are increasingly being used inside hospitals to help manage blood sugar in seriously ill patients. This is a promising idea, since frequent glucose checks are critical in the ICU. But a new 2025 clinical trial asked an important question: are these devices actually accurate enough to be trusted in this high-stakes environment?

Researchers at a hospital setting enrolled 40 critically ill patients who were receiving insulin through an IV drip — one of the most intensive forms of diabetes and glucose management used in medicine. They tested two of the most widely used CGM systems: the Dexcom G6 Pro and the FreeStyle Libre Pro.

What the Study Found

The results raised serious concerns. Both CGM systems showed a surprisingly large gap between what the sensor reported and what laboratory blood tests confirmed as the true glucose level.

• The Dexcom G6 Pro was off by an average of 22.7–22.9% compared to lab and bedside reference readings.
• The FreeStyle Libre Pro was off by an average of 25.2–27.0% compared to the same reference readings.
• Both devices consistently underestimated blood sugar levels — meaning they often showed glucose as lower than it actually was.
• Accuracy varied considerably from patient to patient, making it hard to predict when the sensors would perform well.

To put this in perspective: a 25% error on a blood sugar reading of 200 mg/dL could mean the device displays 150 mg/dL — a difference that could lead to under-treatment of dangerously high glucose levels.

What This Means for Real Patients

For most people managing diabetes at home, CGMs like the Dexcom G6 or FreeStyle Libre are reliable, life-changing tools. MDS Diabetes carries a full range of CGM supplies and sensors for everyday diabetes management, where these devices perform very well.

However, this study highlights that the hospital ICU is a very different environment. Critically ill patients experience changes in circulation, fluid balance, and medication use that can interfere with how CGM sensors read glucose beneath the skin. The researchers concluded that factory-calibrated CGMs may need individual patient calibration — essentially, fine-tuning the sensor against lab results for each specific person — before they can be safely used to guide insulin dosing in the ICU.

Key Takeaways for Patients and Caregivers

• CGMs are excellent tools for home diabetes management but may be less reliable during a serious hospital illness.
• If you or a loved one is in the ICU, ask medical staff how blood sugar is being verified — ideally through lab or fingerstick checks alongside any CGM readings.
• This research does not mean CGMs are unsafe for everyday use outside the hospital.
• Advances in hospital-grade CGM calibration may improve this situation in the future.

Bottom Line

A 2025 clinical trial found that two leading CGM systems — Dexcom G6 Pro and FreeStyle Libre Pro — showed error rates of 22–27% in ICU patients on IV insulin, consistently reading lower than actual blood sugar levels. While CGMs remain valuable for home diabetes care (and MDS Diabetes is here to support those everyday needs), critically ill patients in the hospital may require additional blood glucose verification to ensure safe and accurate insulin dosing.