Switching From Glucose Meters to Continuous Monitors

Medically Reviewed by Minesh Khatri, MD on June 25, 2022
4 min read

You’ve used a blood glucose meter to help manage your diabetes. But now, your doctor may recommend a continuous glucose monitor (CGM) as another way of checking that your blood glucose (also called blood sugar) isn’t too high or low.

Although both devices measure blood sugar, there are some big differences. With blood glucose meters, you prick your finger and the machine tells you the amount of sugar in your blood at that moment. On the other hand, a CGM automatically tracks your blood sugar levels every few minutes, all day and night. This information can show you how your diet, exercise, and habits affect your glucose levels. You and your doctor can use this information to better keep your blood sugar in check.

Because you don’t need to stick your finger as often, many people think CGMs are easier to handle. But getting used to one can take time and patience. The following tips can help you adjust to the change.

Learn how your CGM works. CGMs use a tiny sensor that’s placed just beneath the skin. It measures the glucose in the fluid between cells, called interstitial glucose, every few minutes.

The sensor is attached to a transmitter, which is taped onto the skin. It sends your blood sugar readings to a reader (a small device you can keep in your purse or pocket), smartphone app, or insulin pump. You can download these readings to a computer to look at trends and share the data with your doctor.

There are a few different kinds of CGM systems. Some let you log your meals, exercise, and medicine. This helps you connect the dots between your lifestyle and glucose levels.

Many CGMs have alarms that sound when your blood sugar becomes too high or low. A health care professional, such as your doctor or a diabetes educator, can walk you through how to use your CGM.

Replace your sensor. Depending on your CGM, you’ll need to replace the sensor every 3 to 14 days. You’ll do it on your own with an easy-to-use applicator. Sensors are usually placed on the stomach, thigh, back of the upper arm, or the top of your buttocks.

Your blood sugar measurement can change based on where you put the sensor, so you may have to try a new the location if your readings don’t match your fingerstick values. Don’t place the sensor where you’ll sleep on it regularly or where your clothes can catch on it.

Certain CGM systems have sensors that are placed deeper under the skin by a doctor. They can last for months before you need to replace them.

Factor in a lag time. Fingerstick checks measure your blood sugar at the exact moment you pricked your finger. CGMs examines the glucose in the fluid beneath your skin, so their readings are few minutes behind the actual blood sugar level. They show what your blood sugar was 5 to 10 minutes ago.

This delay usually doesn’t affect how you use your CGM. But it’s important to keep in mind when your glucose may change quickly, such as after taking a dose of insulin or during exercise.

Know that you’ll still need finger sticks. Don’t toss out your blood glucose meter. You may need to use it to “calibrate” your CGM twice a day. That’s when you test a drop of blood on a blood glucose meter and compare that reading with your CGM. Both numbers should be roughly the same.

You may also need to do a finger stick when:

  • You’ve replaced a sensor. For many CGMs, you’ll need to calibrate the sensor within the 2 hours after you insert it.
  • Your blood sugar readings are too low or high.
  • You have symptoms of high or low blood sugar.
  • You think that your readings aren’t accurate.

Don’t change your diabetes care plan. Most of the time, you can’t make changes to your treatment, such as taking an extra dose of insulin, based on CGM readings alone. You’ll need to double-check your blood sugar with a fingerstick blood glucose test.

Right now, the FDA has approved only a few CGMs for guiding treatment decisions on their own. Ask your doctor if your system is one of them.

Work closely with your diabetes team. When you first start using your CGM, you may get higher blood sugar readings than before. This may be because with your blood glucose meter you only tested at specific times. With a CGM, you’re also seeing your levels between finger sticks. Now you may notice blood sugar spikes, like those that happen after meals, that would have been harder to spot using the fingerstick method.

Take note of these falls and peaks in your blood sugar, but don’t panic. You don’t want to react right away by taking in too many carbs or extra insulin. Talk to your doctor about your readings so you can work together to manage your diabetes.