Your numbers include your A1C, which is the three-month average of your blood glucose. It is done as a blood sample from your arm. Measuring your own blood glucose levels at home provides more numbers. There are three ways to measure your blood glucose. For most people living with diabetes, blood glucose readings involve doing a finger stick and using a blood glucose meter. This is referred to as self-monitoring of blood glucose or SMBG.
The FreeStyle Libre flash glucose monitoring system is indicated for measuring interstitial fluid glucose levels in adults aged 18 years and older, who have at least two years of experience in self-managing their diabetes. For In Vitro Diagnostic Use Only. Always read and follow the label/insert for detailed instructions and indication of use.
Less common is using a continuous glucose monitor (CGM),which involves a sensor placed just under your skin. Blood glucose values are drawn from your interstitial fluid. These values are checked every five minutes, and the result is pushed to a reading device or a smart phone. CGM systems have additional functions, including alarms. They also can be built right into an insulin pump system so that only one device needs to be used. The systems need to be calibrated. That means that twice a day, a finger stick blood glucose is done, and the result is entered into the device to ensure that the CGM is accurately measuring the blood glucose readings. These systems record blood glucose values for up to 10 days with a single sensor. The reports can be uploaded into a computer program.
Most recently, flash glucose monitoring has become available. The system is called FreeStyle Libre and is currently the only FGM available in Canada. With flash glucose monitoring, a small sensor is inserted into the back of the upper arm. This sensor stays in place for 14 days. Once a minute it reads the blood glucose from the interstitial fluid.
Blood is pumped from your heart into your arteries and eventually reaches your tiny capillaries. Fluid then moves through the walls of the capillaries and enters into the space surrounding the cells in your body. This space is called the interstitial space. Interstitial fluid (ISF) is important as it provides key nutrients and oxygen to the cells of your body. Eventually, the fluid goes back into your blood system. As it returns to the heart, the whole process starts over.
Think of it like a train going along a track – the first, second and third cars are all basically the same. When the train goes up a hill, the first car is higher than the third car for a little while. Then the third car catches up and is on the same level. When the train goes down a hill, the first car is lower than the third car for a little while, until the third car reaches the bottom of the hill. If the first car is much higher or much lower, it takes the third car a bit longer to catch up. Blood glucose levels follow the same pattern. Your finger stick blood glucose is the first car, and your interstitial blood glucose is the third car. During times of change, especially rapid change, the blood glucose in the interstitial fluid will be different than the capillary blood glucose.
Unlike a CGM system, the flash glucose monitoring system does not require a finger stick to calibrate the device. However, a finger stick blood glucose is recommended during times of rapid change in your blood glucose, or anytime the flash glucose monitor reading does not match your symptoms.
When you do a finger stick, it provides a sample of your capillary blood glucose (CBG). This is rich in oxygen and nutrients. It is also the most up-to-date measurement of your blood glucose, as the blood has just been pumped from your heart. If your interstitial blood glucose is measured during times when your blood glucose is not changing, the glucose value will be very close to the glucose value from your finger stick. However, when your blood glucose is rapidly changing – either dropping or rising – the glucose reading in the interstitial fluid may be a bit slower to change than your finger stick. This is called lag time.
Your sensor and finger stick results may be different on the first day of wearing your sensor. This is related to the sensor settling into the interstitial fluid. It is almost like the sensor is warming up as the interstitial fluid gets it wet, before it starts to read the blood glucose levels consistently. On the first day of sensor use, it is important that you do a finger stick if your blood glucose levels do not match your symptoms.
As mentioned, the glucose values from the CGM sensor are automat-ically pushed to the reading device every five minutes. The FGM sen-sor must be scanned, ‘pulling’ the results to the reader so you can check your blood glucose level. The FGM sensor reads your blood glucose once a minute. It records all blood glucose measurements into the sensor every 15 minutes. As long as you are scanning the sensor at least every eight hours, you will capture your glucose reading that was done every minute. Doing a scan every eight hours records all of your blood glucose levels for the entire day. That means approximately 1440 blood glucose readings are stored in the reader each day. As mentioned, the CGM does have alarm systems built into it for low and high glucose alerts. Currently, the FGM system does not have alarms.
To answer this question, it helps to know what you will see on the reader when you scan the sensor. Below is an example of a scan result from a FreeStyle Libre reader on the left, and one from the FreeStyle Libre iPhone app on the right.
You will see three key pieces of information displayed.
It is important to look at all three to understand the effect that food, activity, stress, illness and medication can have on your blood glucose. Use this information to learn, act and not react. By using the FGM scan frequently, you can start to really understand what is happening with your blood glucose. It gives you more information than you have ever had available before. The key is to learn from it and make changes based on the patterns you start to see. Rather than quickly fixing the highs, you can act based on your understanding of why they are happening. It is very important that you act if your blood sugar is going low or you feel like it is dropping. Do not ignore the symptoms of low blood glucose. It is recommended that you perform a fingerstick to confirm. Proper identification and treatment of low blood glucose levels is important to keep you safe.
An example of an ambulatory glucose profile reading from Glooko and Diasend is available here.
FGM captures about 1440 readings every day. That is a lot of information. Whether you use the FreeStyle Libre or the LibreLink app, the reader will create a variety of reports to help you and your diabetes team use the information to manage your diabetes. These reports include low blood glucose events, time in target range, daily glucose reports, average daily glucose, and a log book. You are also able to enter information, such as insulin doses, food, activity, and other things into the reader that may have affected your blood glucose.
The average daily pattern provides a picture of your blood glucose values for the last 14 days. This is a report that can easily help you identify patterns in your days. You can see areas of low blood glucose (hypoglycemia), fasting and before-meal levels, and after-meal blood glucose levels. Now, you can see how much your blood glucose can vary day to day. More consistent blood glucose readings lead to lower risk of complications, especially for reducing the occurrence of low blood glucose levels.
FGM has been recognized by Health Canada as a replacement for SMBG. Knowing what your blood glucose levels are at various times of the day helps you to understand the effect of food, activity and medications, and to make decisions about them. Even when you are using SMBG to do this, each test presents only one second of any day. Using the flash glucose monitoring system can provide you with so much more information about your blood glucose levels, at the time when you decide you want to know. Research has also shown that using the FGM system can reduce hypoglycemia in people who have type 1 or type 2 diabetes. Learn and act rather than react – it is as simple as a scan.