Denmark Study: Can CGM Monitors Work in Hospital ICUs?

A study from Denmark is asking a critical question that affects thousands of Americans admitted to hospital intensive care units every year: can the same continuous glucose monitors (CGMs) that diabetes patients wear at home actually be trusted when lives are on the line in the ICU?

Researchers at Copenhagen University Hospital-North Zealand conducted a sweeping review of 96 studies to find out — and their findings reveal both promise and important caution.

What the Danish Researchers Did

The Copenhagen team performed what's called a scoping review, systematically combing through medical literature published between December 2023 and May 2024. They analyzed 96 studies examining how accurately CGM devices measure blood glucose in ICU patients compared to traditional blood draws.

Why does this matter? Because in an ICU, blood sugar control is life-or-death serious. Dangerously low blood sugar (hypoglycemia) — anything below 70 mg/dL — or dangerously high blood sugar (hyperglycemia) — above 180 mg/dL — is directly linked to worse patient outcomes, longer hospital stays, and higher death rates. Currently, ICU nurses must draw blood manually, sometimes every hour, to monitor glucose levels. A reliable CGM could reduce patient discomfort and nursing workload dramatically.

What the Danish Team Found

The key accuracy measure researchers used is called Mean Absolute Relative Difference (MARD) — essentially, how far off the CGM reading is from the true blood glucose value. Lower is better. Here's what they found:

• Standard under-the-skin (subcutaneous) CGMs — the type most US patients wear daily — showed accuracy ranging from 6.6% to 30.5% error in ICU settings. That's a wide and concerning range.
• Newer factory-calibrated CGMs (like Dexcom G6/G7 or Abbott FreeStyle Libre, widely used in the US) showed 9.7% to 20.6% error — better, but still variable.
• Intravenous and intra-arterial CGMs, which are inserted directly into blood vessels, performed best at 5–14.2% and 6.4–13% error respectively.

The researchers also flagged a concerning finding: accuracy appeared to drop during hypoglycemia — exactly when precision matters most.

Why This Matters for US Patients

The American Diabetes Association (ADA) and the Society of Critical Care Medicine currently recommend keeping ICU patient blood glucose between 140–180 mg/dL (7.8–10.0 mmol/L), with tighter control for certain patients. Achieving this safely requires accurate, frequent glucose readings.

Millions of Americans living with diabetes — particularly Type 1 — already rely on CGMs like the Dexcom G7 or Abbott FreeStyle Libre 3 for daily management. Many assume these devices will work just as well if they end up hospitalized. This Danish research is an important reality check: your home CGM may not be accurate enough for ICU use without further validation.

The good news is that this review helps map out exactly which CGM technologies show the most promise for hospital use. Intravascular CGMs — while more invasive — demonstrated the strongest accuracy, pointing a clear direction for future ICU technology development.

For US patients and their families, the takeaway is clear: if you or a loved one with diabetes is admitted to the ICU, ask your care team what glucose monitoring method they are using and how frequently they are checking levels. Do not assume your personal CGM device is being used or trusted for critical decisions.

Original Study

Nielsen, Grigonyte-Daraskeviciene, Olsen. "Accuracy of continuous glucose monitoring systems in intensive care unit patients: a scoping review." Intensive Care Medicine (2024). PMID: 39417874. DOI: 10.1007/s00134-024-07663-6