Free Guide to Continuous Glucose Monitors

What Are Continuous Glucose Monitors and How Do They Work

A continuous glucose monitor (CGM) is a small device that tracks blood sugar levels throughout the day and night. Unlike traditional finger-stick tests that give you one reading at a time, a CGM shows you patterns over hours and days. The device uses a tiny sensor that sits just under your skin, usually on your abdomen or arm, to measure glucose in the fluid between cells.

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The sensor measures glucose levels every few minutes—typically every 5 to 15 minutes depending on the device. It sends this information wirelessly to a receiver, smartphone app, or smartwatch. Most CGMs update readings between 288 and 1,440 times per day. This constant stream of data helps you see how food, exercise, stress, and sleep affect your blood sugar.

The sensor itself is about the size of a postage stamp and contains a tiny filament that sits under the skin. This filament measures glucose in interstitial fluid (the fluid surrounding your cells). The readings are typically available within 10 to 15 minutes of when the glucose level actually changes in your bloodstream. Some devices show trends—whether your glucose is rising, falling, or staying steady.

Three major CGM brands are currently available in the United States: Dexcom, Abbott FreeStyle Libre, and Medtronic Guardian. Each system works similarly but has differences in wear time (how long each sensor lasts), accuracy, cost, and app features. Dexcom sensors last 10 days. FreeStyle Libre sensors last 14 days. Medtronic Guardian sensors last 7 days.

A practical takeaway: Before choosing a CGM, learn about the specific features of each brand. Read reviews from actual users and consider which device's app interface makes the most sense to you. Visit the manufacturers' websites to watch demonstration videos showing how sensors are inserted and how the apps work.

Who Uses Continuous Glucose Monitors and Why

Continuous glucose monitors were originally developed for people with type 1 diabetes who need insulin injections or pumps. These devices allow people to adjust insulin doses based on real-time glucose patterns rather than guessing. A person with type 1 diabetes might see that their glucose drops sharply after a certain type of exercise and use that information to take less insulin beforehand.

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Today, CGMs are increasingly prescribed for people with type 2 diabetes as well. Some people with type 2 diabetes take medications that require monitoring, like insulin or GLP-1 agonists. Others use CGMs to understand how different foods and habits affect their glucose levels. Research shows that seeing glucose trends can motivate people to make lifestyle changes, even without medication changes.

Beyond diabetes, some people without diabetes use CGMs to understand their personal glucose patterns. Athletes might track how different meals affect energy levels. People managing prediabetes might use a CGM to see whether their current habits are moving them toward or away from type 2 diabetes. Pregnant people might wear a CGM to monitor gestational diabetes. People with reactive hypoglycemia (low blood sugar reactions) use CGMs to identify triggers.

The data from a CGM can reveal patterns that are invisible with traditional testing. For example, you might discover that your glucose spikes not from carbohydrates but from stress on certain days. You might notice that a particular brand of yogurt causes a different response than another brand with similar nutrition labels. You might find that a 20-minute walk after lunch prevents afternoon energy crashes better than any other time of day.

A practical takeaway: Consider whether you have a specific reason to understand your glucose patterns. If you take diabetes medications, have been told you have prediabetes, are pregnant, or have unexplained energy crashes, a conversation with your doctor about a CGM may be worthwhile. Even if you don't qualify for insurance coverage, understanding your reasons helps you decide whether out-of-pocket costs make sense for your situation.

What Information Continuous Glucose Monitors Display

The main information a CGM shows is your current glucose level in milligrams per deciliter (mg/dL). A normal fasting glucose level for people without diabetes is typically below 100 mg/dL. After meals, glucose can rise to 140 mg/dL or higher in people without diabetes but usually returns to normal within 2-3 hours. The target range varies by individual and by time of day, but people with diabetes often aim for 70-180 mg/dL.

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Beyond the current number, CGMs display trend arrows that show direction and speed of change. An upward arrow means glucose is rising. A downward arrow means it's dropping. A flat arrow means it's stable. Some devices also show the rate of change in mg/dL per minute. This information helps you predict what will happen next. If you see a steep downward arrow, you know low blood sugar is coming and can eat something preventatively.

Most CGMs show hourly and daily patterns in graph form. You can scroll back through your readings to see patterns. You might notice that every Tuesday afternoon your glucose drops, or that a certain restaurant meal always causes a spike. You can compare the same time across different days or weeks. You can see how a new medication or routine change affected your patterns.

CGMs also provide historical summaries showing statistics like average glucose, time spent in range (percentage of time within target glucose), time above range, and time below range. Some devices calculate an estimate of hemoglobin A1c (a three-month average of glucose) based on your CGM readings. Many apps show these statistics weekly or monthly so you can track trends over time.

Many modern CGMs allow you to share data with others. You might share your CGM readings with family members, caregivers, or your healthcare provider. Some devices send alerts to your phone or another person's phone if your glucose gets too high or too low. You can set thresholds for alerts—for example, getting notified when glucose drops below 70 mg/dL.

A practical takeaway: Spend time exploring what your CGM's app actually shows before purchasing or starting one. Request a free trial from the manufacturer if possible. Watch tutorial videos about the specific app you're considering. Understanding the interface helps you know whether you'll actually use the data to make decisions.

Cost, Insurance Coverage, and Payment Options for Continuous Glucose Monitors

The out-of-pocket cost of CGMs varies widely based on your insurance and the specific device. A single sensor can cost between $60 and $100 if purchased without insurance. A receiver device (if the system requires one separate from a phone) costs between $400 and $600. Over a year, a person changing sensors every 10-14 days might spend $2,000-$3,000 out of pocket for sensors alone.

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Many insurance plans cover CGMs for people with type 1 diabetes and some people with type 2 diabetes, particularly those taking insulin. However, coverage rules vary significantly. Some plans require that you first try traditional finger-stick testing for a certain period. Some require prior authorization from your doctor. Some limit which brands they cover. Medicare covers CGMs for beneficiaries with diabetes who take insulin, but specific requirements must be met.

If insurance does not cover a CGM in your situation, several programs may help reduce costs. Most manufacturers offer discount programs directly. Dexcom, Abbott, and Medtronic all have programs offering reduced prices based on income. Some nonprofit organizations related to diabetes provide financial assistance. The Patient Advocate Foundation, American Diabetes Association, and JDRF (formerly Juvenile Diabetes Research Foundation) maintain lists of assistance programs. Some local health departments or free clinics offer information about programs in your specific area.

Some people purchase CGMs through health savings accounts (HSAs) or flexible spending accounts (FSAs), which use pre-tax dollars for medical expenses. This can reduce the effective cost by 20-30% depending on your tax bracket. Some employers offer wellness programs that partially subsidize CGMs. A few companies have begun offering CGMs directly to employees or through employee benefits programs.

The cost-benefit calculation differs for each person. Someone with type 1 diabetes using multiple insulin injections daily may find that better glucose management through a CGM reduces episodes of low blood sugar, prevents long-term complications, and improves quality of life enough to justify the cost. Someone exploring their glucose patterns for general wellness may decide the cost is too high without medical necessity.

A practical takeaway: Contact the manufacturer of each CGM you're considering and ask about their patient assistance programs. Call your insurance directly to