Continuous Glucose Monitoring

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. The sensor sends readings to a receiver, phone, or insulin pump, creating a glucose value, a direction-of-change arrow, and a pattern over hours or days. This distinction matters when glucose is moving quickly. After eating, exercise, a correction dose of insulin, or treatment of hypoglycemia, interstitial glucose may lag behind blood glucose. A sensor value can therefore look lower or higher than the person’s current capillary glucose during rapid change. Some CGM systems display readings continuously and provide alerts for predicted or actual high and low glucose. Intermittently scanned systems require the person to scan the sensor to view readings; alert capability varies by model. Both can reveal patterns that an occasional finger-stick test misses, especially overnight hypoglycemia, post-meal hyperglycemia, and wide glucose variability. A CGM is a trend tool, not a substitute for clinical assessment. A person who is pale, sweaty, tremulous, confused, or unable to swallow may have clinically significant hypoglycemia even if...