If you have diabetes, your blood sugar (glucose) levels tend to change throughout the day. Even when you monitor your glucose often enough (typically four to five times a day), you are getting only a small portion of the whole picture. 

Fortunately, a technological advancement known as continuous glucose monitoring (CGM) is now changing that. 

What’s more, a growing body of evidence shows that this high-tech system is poised to eclipse standard hemoglobin A1C testing, commonly known as A1C, as the gold standard for managing glucose levels. 

If you or someone you love uses insulin to treat diabetes and is not using CGM, it could be time to take the plunge.

What is CGM?

CGM relies on a tiny sensor that you insert yourself into the skin of your upper arm or belly and leave in place for several days. Because the sensor uses a tiny needle, the process is virtually painless. 

The sensor continuously measures glucose in the thin layer of fluid that surrounds the cells beneath your skin—called interstitial fluid—and wirelessly sends the results to a monitor or a smartphone to record your glucose levels 24 hours a day. Results are displayed every few minutes. Retrospective data is also available to detect trends in your glucose levels. 

A CGM device helps you and your doctor create a daily diabetes management plan. It could reduce the frequency (or take the place) of using a glucometer to measure your blood levels of glucose to determine your insulin needs. 

CGM reduces the number of finger sticks typically needed to use a glucometer and test strips by 90%—or by close to 100% for some of the latest devices. The specifics vary among CGM devices, so be sure to discuss these details with your diabetes educator or medical provider. 

An important feature of CGM devices is that they allow the information to be shared with others—for example, parents can monitor a child or adults can track how well elderly parents are controlling their diabetes.

Note: Your doctor may use a professional CGM device to see how well you’re managing your diabetes. You might wear the monitor for days or weeks while trends in your glucose levels are stored in the sensor/device and can be downloaded to your doctor’s computer. People with type 2 diabetes can benefit from this type of periodic monitoring even if they do not need insulin. 

Beyond the A1C test

Since the 1980s, the A1C test has been uniformly used to monitor glucose levels. This simple and inexpensive blood test tells you and your doctor your average blood sugar over an eight- to 12-week period. The A1C test, which usually is performed in a doctor’s office or lab, does this by measuring the percentage of your red blood cells carrying glucose. 

For your glucose management to be effective in preventing complications, most diabetes guidelines recommend an A1C of 7% or less when possible. This goal needs to be personalized to each patient’s circumstances, and it changes over time.

It helps to think of your A1C as a baseball batting average. It tells you how well you are hitting, but it does not tell you when you are getting lots of hits or when you are in a slump. These ups and downs are called glycemic variability. 

That’s where CGM shines. It shows your real-time highs and lows as well as your trends (and averages) over time. Studies show that people with diabetes who use CGM have improved A1C levels and less glycemic variability. 

Why is that important? Research shows that the time you spend in hyperglycemia (glucose levels above 180 mg/dL two hours after eating) is directly related to your risk for diabetes complications, such as heart disease and stroke. 

CGM also shows the time you spend in hypoglycemia (glucose below 70 mg/dL). That can be particularly useful if you have hypoglycemia at night or if you don’t get warning signs of the condition, such as shakiness, dizziness and hunger. 

Unrecognized hypoglycemia can progress to a dangerously low glucose level (below 50 mg/dL), which can cause confusion, heart-rhythm irregularities, blurred vision, accidents, loss of consciousness, seizures and even death. 

A1C also has other weaknesses. Aiming for a reading of 7% or less does not fit everyone. This is especially true for older people who have a naturally higher A1C because they have fewer red blood cells. Forcing these individuals to lower their A1C to 7% or less can increase their risk for hypoglycemia. Additionally, when a person has anemia or other abnormalities of red blood cells, A1C may not accurately estimate the glucose average. 

Who benefits most from CGM?

CGM, which is prescribed by a physician, is for people with type 1 diabetes or those with type 2 diabetes who use multiple daily injections of insulin. The device typically is best for those who require frequent finger sticks (at least four times daily) to control their glucose levels. 

CGM can be especially beneficial for people who unknowingly experience hypoglycemia. Certain devices will warn you of a hypoglycemic trend, and some models will send you and family members a warning alarm if you dip into the danger zone. 

If you use an insulin pump, you should consider a CGM device that is compatible with your insulin pump. Some CGM models and insulin pumps are integrated. Insulin delivery by the insulin pump could be automatically adjusted to prevent or reduce your chances of hypoglycemia.

When using a CGM device, you’ll see in real time how your diet, activities and stress levels affect your glucose levels. With your doctor’s help, you will learn how to anticipate these trends and tweak your insulin use to address them. 

Getting started with CGM 

If you’re interested in trying a CGM device, talk to your doctor and your diabetes educator. If they think that you’d benefit, there are many different devices on the market. 

Some have more bells and whistles, such as alarms for high and low glucose levels…graphs you can download onto your computer or smartphone…and some even are connected to an insulin pump that gives you a glucose reading to use for a programmed dose of insulin for your meal or to correct a high glucose level. 

Not surprisingly, CGM can be ­pricey. Your doctor or diabetes educator can help you select the best model for your needs.* If you go with a basic CGM system and meet the required criteria, it often is covered by insurance. The out-of-pocket cost to use it may not be much more than what you would be paying for a glucometer and your test strips. 

Most CGM devices still require a few finger sticks to ensure that they are accurately reflecting your glucose levels. This is called calibration. Depending on the device you choose, you may need to calibrate occasionally or every day.

Important: There is about a 15-­minute delay for glucose changes in your blood (as measured by a finger stick) to show up in interstitial fluid (as measured by CGM). In certain situations, you may need to do a finger stick before making any insulin dose changes based on just your CGM. (Your doctor or diabetes educator can advise you on managing special circumstances and what’s best for you.) 

Once you start using CGM, the data stored on your monitor will help your doctor recommend the timing and dose you should take of a ­longer-acting or shorter-acting insulin…or adjust the pump setting if you’re using an insulin pump. 

Your job will be to follow your doctor’s insulin directions and to use your readings to make any necessary adjustments to your meals and activity levels. 

*To find a diabetes educator near you, go to the National Certification Board for Diabetes Educators at NCBDE.org/find-a-cde/.