Overview
How the Sensor Sees Glucose
A continuous glucose monitor (CGM) measures glucose in interstitial fluid, the fluid surrounding cells beneath the skin.
A continuous glucose monitor (CGM) measures glucose in interstitial fluid, the fluid surrounding cells beneath the skin. It does not directly measure capillary blood glucose. A small sensor sits under the skin, and a transmitter sends readings to a receiver, smartphone, insulin pump, or other display. This difference matters most when glucose is changing quickly. After a meal, correction dose, exercise, or treatment of hypoglycemia, interstitial glucose may lag behind blood glucose. The displayed number can therefore be temporarily higher or lower than a capillary result. CGM offers more than isolated glucose values. It shows direction and speed of change through trend arrows, helping the person anticipate where glucose may be heading. A reading of 6.0 mmol/L with a rapidly falling trend has a different safety meaning than 6.0 mmol/L with a stable trend. Trend information supports decisions, but it does not replace an individualized insulin or hypoglycemia plan. Confirm with capillary blood glucose when symptoms do not match the CGM reading, when a value seems implausible, during rapid glucose shifts, when the device instructs confirmation, or when required by...