One of the FreeStyle Libre FAQs we get often is about the difference between blood glucose testing (what you do with a fingerstick test) and interstitial fluid – what you get from a flash glucose monitor like the FreeStyle Libre. Here’s a simple explanation of the difference.
Understanding the difference between capillary blood glucose testing and the FreeStyle Libre Flash Glucose Monitoring System
Fingerstick blood glucose readings and sensor glucose readings won’t always match and in fact are likely to be different. That’s because sensor glucose readings come from the interstitial fluid (ISF), a thin layer of fluid that surrounds cells in the tissue below the skin, not from capillary blood.
A 5 to 10-minute delay
There is a 5 to 10-minute delay in interstitial fluid glucose response versus changes in blood glucose. Glucose readings in ISF have been proven to reliably reflect capillary blood glucose levels.
Capillary blood glucose testing provides an instant reading for current glucose levels without providing any information on its progression or trend. The FreeStyle Libre Flash Glucose Monitoring System provides a complete image of the changes in glucose levels during the day and night.
Not all readings are alike
There are a few situations where interstitial fluid glucose levels may not accurately reflect blood glucose levels:
- Hypoglycaemia (low blood sugar)
- Rapidly changing glucose levels
- Postprandially (after a meal)
- During or after participation in sporting activities
Here’s a simple video explanation:
Remember: A fingerstick test using a blood glucose meter is required during times of rapidly changing glucose levels when interstitial fluid glucose levels may not accurately reflect blood glucose levels or if hypoglycaemia or impending hypoglycaemia is reported by the system or when symptoms do not match the system readings.
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