How Do Dexcom’s Work? A Step-by-Step Guide to CGM Basics

Roughly 80% of people living with type 1 diabetes fail to meet their target A1C levels using traditional fingerstick monitoring alone. It is a frustrating reality. You prick your finger, see a number, and wonder what happened in the three hours since your last check. This reactive approach to health often feels like trying to drive a car while only looking through the rearview mirror. But there is a more proactive way to navigate your glucose health. By the end of this guide, you will understand exactly how continuous glucose monitors (CGMs) function and how they can transform your daily management routine.

How Do Dexcom’s Work? A Step-by-Step Guide to CGM Basics starts with moving away from snapshots and toward a continuous movie of your metabolic health. I have found that once patients see their data in real time, the anxiety of the unknown begins to fade. We are going to break down the hardware, the science of interstitial fluid, and how to actually use those trend arrows to make better decisions.

The Core Components

At its heart, a Dexcom system is a three part harmony of technology designed to work around the clock. You have the sensor, the transmitter, and the display device. The sensor is the part that actually lives on your body. It is a tiny, flexible hair like wire that sits just beneath the skin. But here is the thing: it does not stay in your vein. It rests in the fatty tissue.

The transmitter is the gray plastic brain that snaps into the sensor holder. It is responsible for taking the raw data from the sensor and beaming it via Bluetooth to your smartphone or a dedicated receiver. In my experience, the integration with smartphones has been the biggest shift in patient compliance over the last decade. You no longer need to carry an extra pager like device if you do not want to.

• This sensor wire is coated in an enzyme called glucose oxidase
• The transmitter typically lasts about 90 days on older models, while newer versions combine these parts
• Your smartphone acts as the primary interface for alerts and history
• The system updates your reading every five minutes

Everything starts with these pieces working in tandem. If one piece is out of sync, the whole system stalls. This leads to an important question: how does that tiny wire actually get under your skin without a trip to the doctor?

The Insertion Process

Applying a sensor might look intimidating at first. I know what you are thinking: “I do not want to push a needle into my arm every week.” But the modern silk-touch applicators have turned this into a one handed, nearly painless task. You simply clean a patch of skin, place the applicator against your body, and press a button. A hidden needle guides the sensor wire in and then retracts instantly.

What most people miss is the importance of site rotation. If you keep placing the sensor in the exact same spot on your abdomen or arm, you develop scar tissue. This hinders accuracy. I recommend “mapping” your body to ensure you are always at least two inches away from your last site. This keeps the tissue healthy and the readings precise.

• Clean the area with 70% isopropyl alcohol and let it dry completely
• Avoid areas with loose skin, tattoos, or heavy muscle
• Use medical adhesive patches if you have an active lifestyle or sweat heavily
• Wait for the warm up period, which usually takes about 30 minutes to two hours depending on the model

Once that sensor is in place, it begins a chemical conversation with your body. It does not look at your blood directly, which is a common misconception that causes confusion for new users.

Glucose Sensing Technology

The magic happens in the interstitial fluid. This is the clear fluid that surrounds your cells. When you eat carbohydrates, they break down into glucose and enter your bloodstream first. From there, the glucose leaks out into the interstitial fluid. The Dexcom sensor measures the glucose concentration in that fluid.

Building on that, there is a slight time delay. Because glucose hits the blood before it hits the interstitial fluid, your CGM reading might be 5 to 15 minutes behind a fingerstick. This is perfectly normal. In my experience, patients get frustrated when their meter says 120 and their Dexcom says 140. Bottom line? They are both right; they are just looking at different biological “clocks.”

• Interstitial fluid provides a steady stream of data without constant bleeding
• The enzyme on the sensor creates a small electrical current when it reacts with glucose
• This current is measured in nanoamperes and converted into a mg/dL value
• Accuracy is highest when your blood sugar is stable rather than spiking or crashing

Taking this a step further, the system needs to move that data from your arm to your eyes. That is where the wireless communication protocol comes into play.

Data Transmission Steps

The transmitter is constantly working. Every five minutes, it wakes up, gathers the latest electrical signal from the sensor, and packages it into a data packet. It then sends this packet via Bluetooth Low Energy (BLE) to your phone. This specific type of Bluetooth is designed to save battery life, which is why your phone can stay connected all day without dying.

But here is the kicker: the range is usually about 20 feet. If you leave your phone in the kitchen and go to the backyard, you might see a “Signal Loss” alert. Don’t panic. The system is designed to backfill that data once you get back in range. It stores several hours of readings so your graph remains a solid line rather than a series of dots.

• Bluetooth must remain on at all times for the system to work
• Close other high-drain apps to ensure the CGM app stays active in the background
• Set your “Critical Alerts” to bypass your phone’s silent mode
• Use the cloud sharing feature to let family members see your data in real time

This constant flow of data is what allows for the most powerful feature of the system: trend arrows. Understanding these is the difference between reacting to the present and predicting the future.

Interpreting Trend Arrows

A single number on a screen is just a data point. A number with an arrow is actionable intelligence. If your screen says 150, that could mean you are doing great. But if it says 150 with an arrow pointing straight up, you are actually heading toward 200 or higher. Conversely, 150 with a double arrow down means you might be in a hypoglycemic crisis within twenty minutes.

I have found that new users often over-correct. They see a rising arrow and take a massive dose of insulin, only to crash an hour later. Look at it this way: the arrows tell you the velocity of your glucose. One arrow up means your sugar is rising by 2 to 3 mg/dL every minute. Two arrows up means it is rising by more than 3 mg/dL per minute.

• A horizontal arrow means your sugar is stable (changing less than 1 mg/dL per minute)
• Angled arrows indicate a slow rise or fall
• Use arrows to “catch” a low before the alarm even sounds
• Share your trend data with your doctor to adjust your long-acting insulin doses

The takeaway is that you are no longer guessing. You are observing the speed and direction of your health. Armed with that knowledge, you can make small, precise adjustments rather than large, swinging corrections that lead to the “diabetes roller coaster.”

The Evolution of Management

The shift from manual testing to a CGM system represents a total change in lifestyle. It is not just about avoiding needles. It is about the mental freedom that comes from knowing you will be alerted before a dangerous event occurs. For many, the overnight peace of mind is the most significant benefit. Knowing that an alarm will wake you if your sugar drops while you sleep is life-changing.

I have seen patients go from testing 10 times a day to once a week (just to verify the sensor) and their A1C still drops significantly. This happens because the “How Do Dexcom’s Work? A Step-by-Step Guide to CGM Basics” isn’t just about the hardware; it is about the behavior change that follows. When you see exactly how a slice of pizza or a morning jog affects your body, you start making better choices naturally.

• You get 288 readings every 24 hours compared to 4 or 5 with fingersticks
• Most users report a 1% or greater reduction in A1C within the first six months
• The system helps identify “silent” highs and lows you would otherwise miss
• Data can be exported into professional reports for your endocrinology visits

Transitioning to this technology is a learning curve, but the results speak for themselves. You gain a level of control that was simply impossible twenty years ago. You are moving from a reactive state to a proactive one.

Putting It All Together

Understanding how these devices work is the first step toward reclaiming your time and energy from the demands of diabetes. We have covered the physical components, the insertion, the science of the fluid, and how to read the trends. The system is built to be your silent partner, watching your back while you go about your day.

The transformation here is simple: you stop being a passenger in your own health and start being the pilot. You have the data. You have the alerts. You have the trends. Now, you just need the right tools in your hands to make it happen.

If you are ready to stop the constant fingersticks and start seeing the full picture of your health, St. Joseph Medical can help. We specialize in providing the latest glucose monitoring technology, including the FreeStyle Libre 3 and Dexcom G7, to ensure you have the best tools for your specific needs. Our team works with you to navigate the setup and ensure you are getting the most out of your device. Reach out to St. Joseph Medical today to see how we can simplify your diabetes management.