By now most of you have heard about Continuous Glucose Monitors (CGMs) that allow you to monitor your sugar without fingersticks. It’s true! There are several systems currently available in the U.S. marketplace. What they all have in common is that you wear a disposable sensor on your body and the glucose readings are transmitted wirelessly to a receiver. The sensor is a thin filament that is inserted just under the skin. The receiver is a separate device that is roughly the size of a standard glucose meter or your own smart phone.
Today, I am going to tell you about the FreeStyle Libre 14 day system. This CGM works for 14 days after a 1 hour warm up period. The sensor is inserted into the back of the upper arm. It is waterproof (for up to 30 minutes, up to 3 feet deep) and discreet. After the warm up period, the sensor measures the glucose in your tissue fluid every minute! You see these readings only after holding a reader (the receiver or an iPhone) over the sensor for 1 second.
There is even an App to use your iPhone to look at your CGM readings. The FreeStyle LibreLink app is compatible only with iPhone 7 and later (running iOS 11 and later). (Sorry Android users!) In addition to you being able to see the readings on your phone, you can also designate up to 20 others who can also access your glucose data via their iPhones. Remember, none of the data is available for review in the App until you actively scan over your sensor with your phone.
Fingersticks are not generally needed after the warm up period. The FreeStyle sensor is factory calibrated and needs no additional calibrations while being worn. Fingersticks are still required for treatment decisions if there is a “check blood glucose” symbol displayed on the reader, when you are having symptoms that do not match the CGM readings, when you think the system might be giving an inaccurate reading, or if you are having symptoms that might be due to a high or low blood sugar. The reader has a built in blood glucose meter, so you don’t need a separate meter. This meter uses only the FreeStyle Precision Neo test strips. If those strips are not covered under your health insurance, you can use any meter your insurance covers.
IT’S NOT PERFECT
If you have high blood levels of ascorbic acid (Vitamin C) or salicylic acid (aspirin) in your body, these can interfere with sensor glucose readings, but acetaminophen (Tylenol) won’t interfere. If your blood sugar is under 40, “LO” is displayed on the reader. If your blood sugar is over 500, “HI” is displayed. The FreeStyle also tends to overcall hypoglycemia. In a study, 40% of the time that the Freestyle indicated the glucose was under 60 mg/dL, it was actually 81 mg/dL or higher. This means that you would need to look at your glucose trend, assess your symptoms, and perhaps do a fingerstick blood glucose reading if the FreeStyle shows that your glucose is low.
Your CGM sensor glucose readings may not exactly match your fingerstick blood glucose readings if tested at the same time. In part, this is due to the glucose being measured in blood versus in tissue fluid (called “interstitial fluid” or ISF). The glucose has to move from your bloodstream into your tissues and this takes several minutes. If your blood glucose level is changing quickly, the change is not reflected in the ISF for several minutes. Also, even though the system checks your glucose reading every minute, it stores the data for later retrieval only every 15 minutes. This means the glucose shown on the reader when you scan is the current one (within the last minute), but the tracing of your glucose readings over time reflects 15 minute intervals.
Here are some people who should not use the FreeStyle Libre: kids under age 18, pregnant women, people on dialysis, or critically ill persons. Also, this system is not able to proactively alert you if your glucose level is too low or too high. You have to scan with the reader or your iPhone App to see what your glucose is doing. For people who are unable to feel a low blood glucose level, a different CGM that can alert you with alarms may be a better choice. For everyone else, this is a good CGM to consider getting.
The next generation of the FreeStyle Libre, the FreeStyle Libre 2, will offer customizable alarms for low glucose and high glucose, as well as an alert if the sensor is not communicating with the reader. In any of these events you will be notified through sound or vibration, but you will still need to scan your sensor (or check your blood sugar with a meter) to get a reading. The FreeStyle Libre 2 has been approved in Europe and should be available in the U.S. very soon.
HOW TO GET ONE
If you want to get a FreeStyle Libre 14 day system of your own, you will need prescriptions from your healthcare provider for both the reader (only 1 needed every year) and the sensors (2 per 28 days). Most commercial insurance plans will cover this for you. Medicare provides coverage if several criteria are met and documented in your doctor’s office note: you have diabetes and have already been testing with a regular blood glucose meter 4 or more times daily and are taking 3 or more daily injections of insulin or are using a Medicare-covered insulin pump and your insulin dose needs “frequent” adjustments. You will need to see the treating healthcare provider at least every 6 months to continue to qualify.
Using a CGM can be an eye-opening experience into your glucose control that gives you minute by minute feedback on how your actions affect your glucose readings. You don’t know what you don’t know, but, with a CGM, you will know exactly what your glucose levels are doing.