CGM Goals Are Linked — Except for Low Blood Sugar

What This Study Found

A large real-world study of over 56,000 people with type 1 diabetes using an automated insulin delivery (AID) system found that most continuous glucose monitoring (CGM) targets are closely linked to each other. If your Glucose Management Indicator (GMI) is on track, you are very likely meeting targets for time in range and time spent above healthy glucose levels. However, time spent in low blood sugar (hypoglycemia) does not follow the same pattern — it behaves independently and needs to be watched separately.

Why This Matters for You

If you use a CGM and an automated insulin pump (sometimes called a closed-loop or AID system), your care team reviews several numbers at once. This study shows that many of those numbers rise and fall together, which is reassuring. But there is an important exception: how often your blood sugar goes low is not automatically fixed just because your overall control looks good.

Think of it this way — you could have a great A1C-estimated score (GMI) and still be having too many low blood sugar episodes. This study confirms that low blood sugar risk is a separate problem that deserves its own focus, no matter how good your other numbers look.

What the Researchers Did

The research team analyzed real-world CGM data from the Medtronic 780G AID system — a device that automatically adjusts insulin based on glucose readings. They looked at data from:

• 41,692 people over age 15
• 14,459 people age 15 and under

They examined how seven common CGM measurements related to each other, including time in range (TIR), time in tight range, time above 180 mg/dL, time above 250 mg/dL, time below 70 mg/dL, time below 54 mg/dL, and GMI.

Key Numbers From the Study

For adults aiming for a GMI below 6.5% (similar to an A1C of 6.5%), the study found you would likely need:

• More than 81% time in range (70–180 mg/dL)
• More than 58% time in tight range (70–140 mg/dL)
• Less than 15% time above 180 mg/dL
• Less than 1.9% time above 250 mg/dL

These targets predicted each other with over 90% accuracy. But time spent below 70 mg/dL showed only a weak connection to GMI — meaning good overall control does not protect you from lows.

What This Means in Plain Terms

Your CGM gives you a lot of data, and it can feel overwhelming. This study offers a helpful simplification: if your GMI or TIR is on target, most of your other high-glucose numbers are probably in good shape too. But always ask your care team about your low blood sugar time separately — it will not take care of itself.

How MDS Diabetes Can Help

Managing all these CGM metrics starts with having reliable supplies. MDS Diabetes (mdsdiabetes.com) carries CGM sensors, insulin pump supplies, and diabetes management tools to help you stay consistent with your monitoring routine — because accurate data is the foundation of good control.

Citation: Castañeda, de Galan, van Kuijk (2024). The interdependence of targets for continuous glucose monitoring outcomes in type 1 diabetes with automated insulin delivery. Diabetes, Obesity & Metabolism. PMID: 39323365. DOI: 10.1111/dom.15955