Continuous glucose monitoring

Overview

Continuous glucose monitoring (CGM) is a wearable device that checks your blood sugar (glucose) levels day and night. A small sensor under your skin sends readings to a display, like a phone or receiver, so you can see patterns and avoid highs and lows.

More and more people with diabetes—especially those on insulin—are using CGM. The NHS and health services worldwide now offer it to many patients.

CGM is mainly used by people with Type 1 diabetes and those with Type 2 diabetes who need insulin or have trouble with glucose swings. It can also help pregnant women with diabetes and some children.

Symptoms

Common symptoms

• Feeling shaky, sweaty, or dizzy (low blood sugar)
• Feeling very thirsty, needing to urinate often (high blood sugar)
• Tiredness or blurry vision when sugar levels change

Symptoms in children

• Sudden moodiness or irritability
• Complaints of headache or stomach ache
• Having trouble concentrating at school

Symptoms in older adults

• Confusion or drowsiness without other cause
• Falls or feeling unsteady
• Slower recovery from illness or infection

Causes

Main causes

• Diabetes – either Type 1 or Type 2 – causes unstable glucose levels.
• Insulin or other blood sugar-lowering medications can lead to lows.
• Exercise, food, stress, and illness can make glucose change quickly.

Risk factors

• Taking insulin injections or using an insulin pump
• Not feeling symptoms when blood sugar is low (hypoglycemia unawareness)

When to see a doctor

See a doctor urgently if:

• If your CGM shows very low or very high numbers that won't improve
• If you have symptoms of severe low blood sugar (confusion, seizure)
• If the sensor area becomes red, swollen, or painful

Book a routine appointment if:

• Talk to your doctor if you are interested in starting CGM.
• If you already use CGM, have a regular review of your readings and settings.

Diagnosis

CGM is not a diagnosis for diabetes, but a tool used after you are diagnosed. Your healthcare provider will prescribe a CGM system if they think it will help you manage your blood sugar better.

Tests that may be done

• A blood test (HbA1c) to see your average glucose over 3 months
• Finger-stick checks to confirm sensor accuracy in the first few days
• A clinic visit to learn how to insert the sensor and use the app or receiver

What to expect at your appointment

You'll be shown how to put the small sensor on your skin (usually on your upper arm or belly). It will start reading glucose levels within an hour. You'll see real-time numbers and trends on your phone or a separate device. Your care team will help you interpret the data and adjust your treatment plan.

Treatment

CGM itself is not a treatment, but it guides your diabetes treatment. The information it provides helps you and your healthcare team make better decisions about insulin, meals, and physical activity to keep your blood sugar in a healthy range.

Self-care at home

• Check your CGM readings regularly throughout the day and night
• Respond to high or low alerts quickly with glucose or insulin as advised
• Keep the sensor site clean and dry to avoid skin irritation
• Share your CGM data with your doctor or diabetes nurse for review

Medical treatments

Based on CGM data, your doctor may adjust your insulin doses, suggest changes to your diabetes medication (taken by mouth or injection), or help you fine-tune your meal timing. Some people use the CGM with an insulin pump to automatically adjust insulin delivery (a hybrid closed-loop system).

Living with this condition

Wearing a CGM sensor becomes routine. You can shower, swim, and exercise with it on. The device will alert you if your glucose is going too high or too low, so you can take action quickly. Many people feel safer and less worried about severe lows.

Lifestyle tips

• Keep a small supply of fast-acting sugar (like juice or glucose tablets) with you in case of lows
• Avoid sleeping on the sensor if it feels uncomfortable
• Make sure your phone or receiver is charged and within range
• Tell teachers, coworkers, or family about your CGM and what the alarms mean

Diet and exercise

CGM helps you see how different foods and exercise affect your blood sugar. You can learn which meals cause spikes and how much physical activity lowers your glucose. This allows you to adjust your diet and timing more precisely. Always speak to a dietitian or diabetes educator for personal advice.

Prevention

CGM is not something that needs prevention – it's a device used to prevent complications of diabetes. Using CGM can help prevent dangerous low blood sugar episodes and reduce the risk of long-term damage from high blood sugar.

Vaccines

Not applicable.

Screening programmes

If you have diabetes, your doctor will check your HbA1c regularly. They may recommend CGM if you meet certain criteria, such as having frequent hypoglycemia or difficulty controlling your glucose despite multiple daily injections.

Complications

If left untreated

• Without proper glucose management, you risk severe low blood sugar (hypoglycemia) that can cause fainting or seizures.
• Long-term high blood sugar can damage eyes, kidneys, nerves, and blood vessels.
• Repeated highs and lows can lead to hospital visits and reduced quality of life.

Long-term outlook

Using CGM can greatly improve your diabetes control and daily life. Most people find it easier to keep their glucose in a safe range, experience fewer severe lows, and feel more confident. With the right support, CGM helps you live well with diabetes.

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