Continuous Glucose Monitoring (CGM)

What it is

A small sensor (Dexcom, Libre, Stelo) inserted in subcutaneous tissue that measures interstitial-fluid glucose every 1–5 minutes for ~10–14 days. Smartphone apps display real-time and trend data.

Why CGM matters in diabetes

• Replaces or complements fingerstick measurements.
• Reveals overnight, post-meal, and hypoglycaemic excursions.
• “Time in range” (TIR) 70–180 mg/dL is a key metric; higher TIR predicts fewer complications than HbA1c alone.
• Used with insulin pumps for hybrid closed-loop dosing.

CGM in non-diabetics

Brands like Levels, Stelo, and others market CGMs to non-diabetics for personalising food choices. The evidence:

• CGM in non-diabetics does show large individual variation in post-meal glucose responses to the same food (the “personalised nutrition” idea).
• Whether using CGM data changes hard endpoints (weight, HbA1c, T2D incidence, cardiovascular events) in non-diabetics is not established.
• Many spikes seen in non-diabetic CGM use are within physiological norms and don’t indicate disease.
• Cost is significant.

Reasonable use cases in non-diabetics

• Investigating unexplained energy / mood fluctuations.
• Pre-diabetic adults wanting concrete feedback on lifestyle changes.
• N-of-1 experimentation with specific foods or meal timing.
• Pregnancy-related glucose monitoring.

Less reasonable: long-term obsessive optimisation in metabolically healthy adults.

Related entries

HbA1c, Fasting insulin, Levels (clinic).