Interstitial glucose lags blood glucose by several minutes, more when glucose is changing fast — after meals, during exercise, and while treating a low. Sensor accuracy is also weakest at the extremes, where decisions matter most.
So confirm with a fingerstick when symptoms do not match the reading, before treating a suspected low that the sensor reports as normal, and when a sensor is new or has just been knocked. Some medicines, notably high-dose vitamin C and paracetamol with certain sensor models, can distort readings; check the device information.
And a sensor does not replace HbA1c: the two answer different questions, and a mismatch between them is itself worth exploring.
- Confirm with a fingerstick when symptoms and sensor disagree
- Expect lag after meals, exercise and treatment of hypoglycaemia
- Check the device leaflet for interfering medicines
- Keep HbA1c in follow-up; a sensor–HbA1c mismatch deserves a look
Why it matters
As sensors spread to people not on insulin, more clinicians will be reading them for the first time.
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