How it works
A thin sensor worn on the arm or abdomen measures glucose in the fluid under the skin every few minutes and sends readings to a phone or reader. Most sensors last 10 to 15 days, depending on the device.
What you can see
- Your current glucose and which way it is heading
- Alerts for highs and lows, including at night
- Time in range: the share of the day between 70 and 180 mg/dL
For many adults with diabetes, a common goal is more than 70% of time in range and less than 4% below 70 mg/dL. Targets are different in pregnancy, in older adults and for people at high risk of lows.
Who may benefit most
- People with type 1 diabetes
- Anyone using insulin
- People with frequent or night-time lows
- Those with swinging sugars that HbA1c does not explain
- People for whom HbA1c is unreliable, such as with anaemia or kidney disease
- People who want a short trial to see how food and activity affect them
Limits
- Sensor readings lag behind blood by several minutes
- A finger-prick is still needed if symptoms do not match the reading
- Cost, and occasional skin irritation from the adhesive
- It does not diagnose diabetes
Getting the most from it
Look at patterns over two weeks rather than reacting to each number, and review the report with your doctor. HbA1c and CGM work best together.
How to read a sensor report
Do not judge control from one high or low reading. A useful review usually looks at at least 10 to 14 days of data, with the sensor active for most of that time. The ambulatory glucose profile can show overnight patterns, rises after meals and periods when glucose is falling too low. Bring the report and your medication list to the appointment.
Time in range is only one part of the picture. Time below range, repeated overnight lows, glucose variability and the pattern of readings all matter. A target that is suitable for one adult may be unsafe for someone who is frail, pregnant or prone to severe hypoglycaemia.
Can a sensor replace every finger-prick?
Not always. Follow the instructions for the specific device. If symptoms do not match the sensor value, glucose is changing rapidly, or the device gives an unexpected reading, confirm with a finger-prick when advised. Do not delay treatment of suspected severe hypoglycaemia while waiting for a sensor reading.
This guide is for general educational purposes and does not replace individual medical advice, diagnosis or treatment. Consult your doctor for advice specific to your health.