Insulin Pumps and Glucose Sensors: How Do They Work?

What is an insulin pump and how does it work?

An insulin pump is a small device that delivers rapid-acting insulin throughout the day and night.

Instead of taking a separate injection of long-acting insulin, the pump delivers small amounts of insulin continuously. This is known as the basal rate.

Additional insulin can then be delivered as a bolus, for example around meals or to correct a high glucose level. The settings and insulin doses are individual and should be agreed upon with the diabetes care team.

There are different types of insulin pumps. Some use tubing connected to a small cannula placed under the skin, while patch pumps attach directly to the body without external tubing.

Using an insulin pump does not mean diabetes management becomes completely automatic. Depending on the system, users may still need to count carbohydrates, enter information about meals, and make decisions about insulin with guidance from their diabetes care team.

If you would like to understand another way insulin can be delivered, Carenity's article The insulin pen for diabetes: Everything you need to know! explains how insulin pens work and how they differ from other insulin delivery methods.

What is a continuous glucose monitor (CGM)?

A continuous glucose monitor, or CGM, is a small wearable device that tracks glucose levels throughout the day and night.

A small sensor sits just under the skin, usually on the arm or abdomen depending on the device. Importantly, a CGM does not measure glucose directly from the blood. It measures glucose in the interstitial fluid, the fluid surrounding the body's cells.

The sensor sends glucose information to a compatible smartphone, receiver, or, with some systems, an insulin pump.

Depending on the type of glucose sensor, users may be able to see:

• Their current glucose reading,
• Whether glucose is rising or falling,
• Glucose trends throughout the day and night,
• Patterns after meals or physical activity,
• Time spent within their individual target glucose range,
• Alerts when glucose is predicted to become too high or too low.

This information can help people understand not just what their glucose level is, but also where it may be heading.

Is a CGM the same as a fingerstick blood glucose test?

Not exactly.

A fingerstick test measures glucose in the blood at that particular moment. A CGM measures glucose in interstitial fluid and provides readings and trends throughout the day.

Because glucose takes time to move between the blood and interstitial fluid, sensor glucose can lag slightly behind blood glucose, particularly when glucose levels are changing quickly.

This means there may still be situations where a fingerstick test is needed. The instructions vary between devices, so users should follow the guidance for their particular CGM and the advice of their diabetes care team.

If a sensor reading does not match how you feel, do not simply ignore your symptoms. Follow the instructions provided for your device and seek medical advice when necessary.

What is the difference between CGM and flash glucose monitoring?

You may hear several terms when discussing glucose sensors, including real-time CGM and intermittently scanned or flash glucose monitoring.

A real-time CGM (rtCGM) automatically sends glucose readings to a compatible device at frequent intervals.

Traditionally, a flash glucose monitor, also known as intermittently scanned CGM, requires the user to scan the sensor to see a reading. However, newer systems may transmit readings automatically when used with compatible devices, so the distinction is becoming less obvious.

Both technologies can provide information about glucose patterns and trends.

The most suitable option depends on individual needs, the diabetes treatment being used, device compatibility, and what is available through local health care services.

Can an insulin pump and glucose sensor work together?

Yes, and this is where diabetes technology becomes particularly interesting.

Some compatible insulin pumps and continuous glucose monitors can communicate with each other.

When a CGM, insulin pump, and computer algorithm work together, this is known as a hybrid closed-loop system or automated insulin delivery (AID) system.

The glucose sensor continuously provides information about glucose levels. An algorithm analyzes those readings and instructs the insulin pump to adjust insulin delivery in response.

For example, depending on the system, it may increase, reduce, or temporarily suspend insulin delivery based on glucose readings and predicted changes.

You may also hear hybrid closed-loop technology described as an “artificial pancreas.” However, this name can give the impression that technology manages diabetes completely independently.

It does not.

Current hybrid closed-loop systems still require input from the person using them. For example, users generally need to provide information about meals and carbohydrates and may need to tell the system about exercise.

What are the potential benefits of insulin pumps and CGMs?

Diabetes technology is designed to support glucose management, but the experience is individual.

Depending on the device and the person using it, possible benefits may include:

• Seeing glucose trends throughout the day and night,
• Receiving alerts for high or low glucose,
• Reducing the need for frequent fingerstick checks,
• More flexible insulin delivery,
• Spending more time within the recommended glucose range,
• Reducing some episodes of hypoglycemia,
• Giving the diabetes care team more detailed glucose information,
• Reducing some of the day-to-day burden of diabetes management.

Hybrid closed-loop systems can take this further by automatically adjusting insulin delivery in response to sensor readings.

However, no device guarantees perfectly stable glucose levels, and diabetes technology still requires learning, monitoring, and ongoing support.

What are some of the challenges of diabetes technology?

For some people, using a CGM or insulin pump can make diabetes management feel easier. For others, adapting to a device that is attached to the body throughout the day can take time.

Possible challenges include:

• Getting used to wearing a device,
• Skin irritation or problems with adhesives,
• Sensors or infusion sets becoming loose,
• Alarms becoming distracting or overwhelming,
• Technical problems or lost connections,
• Learning how to interpret glucose trends,
• Keeping devices charged or carrying supplies,
• Managing devices during exercise, travel, or sleep.

There can also be an emotional side to having glucose information available almost constantly. For some people, seeing every rise and fall is reassuring; for others, it can initially feel like a lot of information.

Neither reaction means someone is managing their diabetes “better” or “worse.” Finding the right technology and learning how to use it confidently can take time.

What happens if an insulin pump or glucose sensor stops working?

Having a backup plan is particularly important for people using an insulin pump.

Because pumps generally deliver rapid-acting insulin rather than a separate long-acting insulin dose, an interruption in insulin delivery can lead to glucose levels rising and, in some situations, ketones developing more quickly.

Users should know what their diabetes care team recommends if:

• The pump stops delivering insulin,
• An infusion set becomes blocked or disconnected,
• A sensor fails or gives unexpected readings,
• Glucose remains unexpectedly high,
• Ketones are present,
• They cannot access their usual diabetes technology.

Do not change insulin doses or settings based solely on general online information. Your diabetes care team can help you create an individualized backup plan and explain when to check ketones, use an alternative insulin delivery method, or seek urgent medical help.

Thinking about a pump or CGM? What should you ask your diabetes care team?

Choosing diabetes technology is not only about which device has the most features. It should fit your treatment needs and, as far as possible, your everyday life.

Before an appointment, you might want to note:

• How often you experience high or low glucose levels,
• Whether you recognize symptoms of hypoglycemia,
• What you find most difficult about your current diabetes management,
• Your experience with fingerstick testing or CGM,
• Your usual physical activity,
• Whether alarms would be useful to you,
• How comfortable you feel wearing a device,
• What you would most like technology to help you with.

You could also ask your diabetes care team which devices are available to you, whether a pump and CGM are compatible, what training is provided, and what to do if the technology fails.

Access to insulin pumps, continuous glucose monitoring, and hybrid closed-loop systems in the United States can vary depending on health insurance coverage, the type of diabetes, individual clinical needs, and the technology involved.

What is it really like to live with a CGM or insulin pump?

Specifications can tell you how a device works, but they cannot always tell you what wearing one every day feels like.

Some people value glucose alerts and being able to see trends without repeated fingerstick tests. Others talk about practical issues such as keeping sensors attached, skin reactions, alarms, or getting used to having technology on their body.

Carenity members have shared their own experiences with insulin pumps in the discussion Voice Your Opinion: Advantages / Disadvantages of Insulin Pumps

Reading other people's experiences can help you think of practical questions you may want to ask your diabetes care team. But the device that works well for one person may not be the right option for another, so treatment decisions should always be individual.

Diabetes technology is a tool, not a test of how well you manage diabetes

Insulin pumps and glucose sensors have changed the way many people manage diabetes. Hybrid closed-loop systems are taking that technology further by allowing compatible pumps and sensors to work together and automate part of insulin delivery.

But using more technology does not make someone “better” at managing diabetes, and choosing injections or another monitoring method does not mean someone is doing something wrong.

The best diabetes technology is the technology that is medically appropriate, safe, and manageable for the individual using it.

If you are interested in an insulin pump, CGM, or hybrid closed-loop system, speak to your diabetes care team about the options available and what may suit your needs.

Frequently Asked Questions

1. What is the difference between an insulin pump and a glucose sensor?

An insulin pump delivers insulin. A glucose sensor or CGM measures glucose levels in interstitial fluid and shows glucose readings and trends. They perform different jobs, although compatible devices can sometimes work together.

2. Does a CGM measure blood sugar directly?

No. A CGM measures glucose in the interstitial fluid beneath the skin. This can sometimes lag slightly behind blood glucose, especially when glucose levels are changing quickly.

3. Does an insulin pump automatically control glucose levels?

A standard insulin pump does not automatically manage glucose by itself. Compatible pumps can form part of a hybrid closed-loop system that uses CGM readings and an algorithm to automatically adjust some insulin delivery.

4. Do you still need to count carbohydrates with a hybrid closed-loop system?

Generally, yes. Current hybrid closed-loop systems still require some user input, including information about meals or carbohydrates, although exact requirements depend on the system.

5. Can everyone with diabetes get an insulin pump or CGM in the United States?

Access and coverage vary according to the type of diabetes, individual clinical needs, age, health insurance coverage, and the technology involved. Speak to your diabetes care team and insurance provider about the options available to you.