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Understanding Continuous Glucose Monitors: What They Are and How They Work

A continuous glucose monitor, often called a CGM, is a small device that tracks your blood sugar levels throughout the day and night. Unlike traditional finger-stick tests that give you a reading at one moment in time, a CGM provides readings every few minutes, usually every 5 to 15 minutes depending on the brand. This constant stream of information shows you how your blood sugar changes in response to food, exercise, stress, and sleep.

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The device consists of three main parts: a sensor that you wear on your skin, a transmitter that sends data wirelessly, and a receiver or smartphone app where you see your readings. The sensor is a thin filament, about the size of a thin noodle, that sits just under your skin and measures glucose levels in your interstitial fluid, which is the fluid between your cells. Most sensors stay in place for about 10 to 14 days before needing replacement.

CGMs were originally developed for people with type 1 diabetes to help them manage their condition more effectively. Over time, they became available for people with type 2 diabetes as well. More recently, some CGM systems have become available to people without diabetes who want to understand their blood sugar patterns and overall metabolic health. The technology has improved significantly over the past decade, with sensors becoming smaller, more accurate, and easier to use.

The way a CGM works is straightforward. When you insert the sensor under your skin, it begins measuring glucose levels in the fluid surrounding your cells. The transmitter, which sits on top of the sensor, picks up these measurements and sends them to your phone or a dedicated receiver. You can see your current glucose level, recent trends showing whether your blood sugar is rising or falling, and historical data over hours or days. Many CGMs also alert you if your blood sugar goes too high or too low.

Practical Takeaway: Understanding the basic mechanics of how a CGM works helps you know what information the device can and cannot provide. A CGM shows you your blood sugar patterns but does not diagnose diabetes or replace blood tests ordered by your doctor. It is a tool for gathering information about how your body responds to different foods, activities, and life situations.

Current CGM Options Available on the Market

Several CGM systems are available in the United States, each with different features, costs, and wearing periods. The most widely known brands include Dexcom, FreeStyle Libre, Medtronic Guardian, and Eversense. Each system has its own characteristics, and understanding the differences can help you learn what features matter most to you.

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The Dexcom G6 and newer G7 models are designed primarily for people with diabetes but have gained attention for their accuracy and user-friendly interface. The G7 sensor lasts 10.5 days and sends readings to your smartphone every five minutes. It includes optional alerts if your blood sugar rises or falls outside your target range. The G6 has similar features but requires calibration with finger-stick tests in some circumstances. Both systems have a transmitter that sits on top of the sensor and communicates wirelessly with your phone or receiver.

The Abbott FreeStyle Libre system works differently from Dexcom. Instead of sending readings automatically to your phone, you scan a small sensor with your phone or a dedicated reader to get your current blood sugar level. The sensor lasts 14 days, making it one of the longest-wearing options. FreeStyle Libre does not require finger-stick calibrations and has gained popularity among people who prefer not to receive constant notifications.

The Medtronic Guardian system is often used alongside insulin pumps and offers automated insulin delivery options for people using Medtronic pump systems. The Eversense system is implanted slightly under the skin and lasts longer than other options, typically around 90 days, though it requires a small procedure to insert and remove it. This option appeals to people who want fewer sensor changes but can be more involved to use.

Pricing and insurance coverage vary significantly. Some insurance plans cover CGMs for people with type 1 or type 2 diabetes, while coverage for other populations is less common. Out-of-pocket costs can range from several hundred to over a thousand dollars per month depending on the system and your insurance situation. Some manufacturers offer patient assistance programs or cash-pay options at lower prices.

Practical Takeaway: Learning about the different CGM systems available helps you understand what options exist and what features each one offers. When considering a CGM for your own use, you would want to research which system aligns with your lifestyle, learn about costs and insurance coverage specific to your situation, and consult with your healthcare provider about which device might be most appropriate for your needs.

What Information You Can Learn From CGM Data

One of the most valuable aspects of using a CGM is the ability to see patterns in your blood sugar response to different foods, activities, and daily habits. For example, CGM data might show you that your blood sugar rises quickly after eating white bread but stays more stable after eating whole grain bread. Another person might notice their blood sugar drops significantly after a 20-minute walk, while someone else might see minimal change. These individual patterns are different for everyone.

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CGMs show you trends over time, which means you can see whether your blood sugar is steady, rising, or falling at any given moment. This information helps you understand cause and effect. If you eat a certain food and your blood sugar spikes two hours later, you have concrete data showing that connection. You can experiment with different foods, portion sizes, meal combinations, and eating times to see how your body responds. This experimentation might help you make informed choices about your diet.

For people with diabetes, CGM data helps show how well their current treatment plan is working. Healthcare providers look at metrics like time in range, which is the percentage of time your blood sugar stays within your target zone. Someone might have a target range of 70 to 180 mg/dL, and their CGM data would show what percentage of the day they are in that range. This helps doctors and patients see whether medication adjustments might be needed.

CGM data can also reveal how stress, sleep, and exercise affect your blood sugar. You might notice that on days when you sleep poorly, your blood sugar is harder to manage or that your morning readings are higher. You might see that stress before a big presentation causes your blood sugar to rise. Exercise might lower your blood sugar for hours afterward. These connections help you understand your body better and potentially identify lifestyle changes that could help you feel better.

The data from CGMs is presented in various ways: a current number, a trend arrow showing direction, graphs showing readings over hours or days, and weekly or monthly summaries. Many apps allow you to share your data with family members or healthcare providers, which can be helpful for collaborative management of your health.

Practical Takeaway: CGM data provides information about how your individual body responds to food, activity, stress, and sleep. This information can help you make choices that feel right for your body. However, CGM data is informational; it does not diagnose conditions or replace medical advice from your healthcare provider. Using the data to have conversations with your doctor about your overall health is more useful than interpreting the numbers on your own.

Who Might Benefit From Using a Continuous Glucose Monitor

People with type 1 diabetes have been using CGMs for nearly two decades now. Because type 1 diabetes requires multiple daily insulin injections or an insulin pump, blood sugar management is complex and constant. A CGM helps these individuals see how their insulin doses, meals, and activities affect their blood sugar minute by minute. Most insurance plans cover CGMs for people with type 1 diabetes because the devices have been shown to reduce complications and improve quality of life.

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People with type 2 diabetes are increasingly using CGMs as well. Type 2 diabetes is more common than type 1 and develops when the body cannot use insulin effectively or does not make enough insulin. For people with type 2 diabetes who use insulin, a CGM can be similarly helpful to those with type 1. Even for people with type 2 diabetes managed with oral medications or lifestyle changes alone, some find that seeing their blood sugar patterns in real time helps them understand which foods and habits support stable blood sugar levels.

Beyond people with diabetes, CGM use is becoming more common among people interested in understanding their metabolic health. Some athletes use CGMs to see how different foods and training schedules affect their energy levels and performance. Some people with prediabetes, which is when blood sugar levels are higher than normal but not yet in the