The Latest in Monitoring: Continuous Glucose Monitors (CGM)

Chapter 16 · Vihang Rahul Vasa

One of the most remarkable advances in diabetes care in recent years is the Continuous Glucose Monitor, or CGM. Unlike a traditional glucometer that gives you a single reading at a single moment, a CGM is a small, discreet sensor, typically worn on the upper arm or abdomen, that continuously tracks your glucose levels throughout the day and night, every few minutes, and sends the readings to your smartphone or a dedicated reader.

The beauty of a CGM is that it stays with you through every activity. Most modern CGMs can be worn while bathing, swimming, walking in the rain, working, sleeping, driving, and exercising: depending on the model. It keeps monitoring silently in the background. It gives you a complete picture of how your glucose rises and falls across the day, which foods spike you, how your body responds to exercise, and how well your medication is working. This is something a few finger-prick readings a day can never show you.

Two practical questions I am often asked.

Can I wear my CGM during an MRI or CT scan? Usually not. Every sensor I have used came with instructions to remove it before an MRI, and often before a CT scan: check the instructions for your own device, and tell the radiology staff you use one. Be aware: a sensor once removed cannot be reused: so such a scan will cost you a sensor either way. If the situation allows, plan the scan for a day when the sensor is due for a change. In an emergency, sacrifice the sensor: the scan matters more.

Can I wear it through airport security? The normal walk-through metal detector and the hand-held wand are generally fine. The full-body scanner and the baggage X-ray machine are not: ask for a hand check instead. The X-ray point matters for the spare sensors in your bag, not the one on your arm. Follow the instructions that came with your own sensor, and carry a short note from your doctor when you travel (see Chapter 53, Diabetes and Travelling, for the doctor’s letter and what to carry).

Illustration: A person wearing a CGM sensor on the upper arm while playing guitar

Life does not pause for monitoring: a CGM sensor works silently while you do what you love. Image: iStock by Getty Images (licensed).

Licensed stock image, for educational illustration only; it depicts no one connected with this book and endorses no brand, device, or manufacturer.

A Practical Bonus: CGM Readings on Your Car Display

Here is a real-life discovery I made during my Mumbai commutes. With certain CGM apps and modern car infotainment systems, you can configure your live CGM reading to display directly on your car’s screen: right alongside your time, weather, and navigation. For anyone who drives long distances or commutes in city traffic, this can help you stay aware of your glucose trends. An important safety note: do not interact with a phone or vehicle display while driving. If a glucose alert needs your attention or action, respond to it only when safely parked. Road safety always comes first.

Illustration: A car display showing a continuous glucose monitoring reading.

A snapshot from my own car, during a Mumbai traffic jam: my live CGM reading visible right on the car display.

A note on personal equipment: This example reflects my personal car system, CGM device, and phone setup. Every reader’s environment will be different. Before purchasing or installing any such system, please check compatibility with your specific CGM, phone, and car infotainment system. Speak to your CGM provider or check their official app documentation. Explore what works with your setup: the options keep improving every year.

One of the strongest advantages of a CGM is its role in protecting you from hypoglycaemia: a low plasma glucose (blood sugar) episode. Most CGMs can be set to sound an alarm when your glucose drops below a safe level, even while you are asleep. This early warning can be life-saving, giving you precious time to take glucose before the situation becomes serious. When choosing a CGM, a model that allows manual calibration with a gluco strip may prove useful for cross-verification and fine-tuning accuracy to your own body. Ask your diabetes specialist to recommend the right CGM for you, based on what is easily available in your city or area.

Illustration: Chapter 16 illustrated summary. Continuous glucose monitoring follows meals, movement, sleep, day and night trends, and possible low alerts.

Chapter 16 Continuous glucose monitoring follows meals, movement, sleep, day and night trends, and possible low alerts. Suitability and device guidance are individual.

Chapter at a glance: an AI-generated illustration to be read with the chapter, not instead of it. The people shown are not real.