How Accurate Is CGM During Low Blood Sugar?

What This Study Found

Researchers tested how accurate continuous glucose monitors (CGMs) are when blood sugar drops into the low range — called hypoglycemia. They found that CGM accuracy was acceptable for people with diabetes using insulin, but became much less reliable when blood sugar fell very quickly. The faster glucose dropped, the more likely the CGM was to give a reading that didn't match the true blood sugar level.

Why This Matters for You

Millions of people with diabetes rely on CGM devices every day to catch dangerous lows before they cause symptoms. This study gives us a clearer picture of when you can trust your CGM — and when you might want to double-check with a finger-stick test.

What the Researchers Did

The study looked at 92 people who experienced low blood sugar in three different situations:

• People with diabetes on insulin injections — the most common real-world scenario
• People with insulinoma — a rare tumor that causes the body to make too much insulin
• People undergoing insulin tolerance testing (ITT) — a medical test where insulin is given on purpose to make blood sugar drop quickly

Researchers compared CGM readings to finger-stick lab values taken at the same time — over 460 pairs of readings in total.

What They Found

The results showed a clear pattern: CGM accuracy depended heavily on how fast blood sugar was falling and why it was low.

• People with diabetes on insulin: The CGM was off by about 13.9% on average — considered acceptable for real-world use. About 82% of readings landed within 20 mg/dL of the true value.
• People with insulinoma: Results were similar and also considered acceptable.
• People during insulin tolerance testing: Accuracy dropped sharply. The CGM was off by more than 50% on average, and only 67.5% of readings were close to the true value.

The study also found that when blood sugar was falling rapidly, CGMs were more likely to underestimate how low glucose actually was — potentially missing a dangerous situation.

What This Means in Plain Terms

Your CGM is a valuable tool, but it's not perfect — especially during a fast-moving low. If you feel symptoms of hypoglycemia but your CGM shows you're in range, trust your body. A quick finger-stick check with a traditional blood glucose meter can confirm what's really happening.

This is especially important if you're prone to rapid drops — for example, after exercise or a missed meal combined with insulin.

A Note on CGM Supplies

Getting the most from your CGM starts with having reliable supplies on hand. At mdsdiabetes.com, you'll find CGM sensors, glucose meters, and testing strips to help you monitor your blood sugar with confidence — whether you're checking your device or double-checking it.

Citation: van Baal, Raess, Mathew (2026). Accuracy and reliability of a continuous glucose monitoring system with a focus on hypoglycaemia. Diabetes, Obesity & Metabolism. PMID: 41448958. DOI: 10.1111/dom.70408