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My Freestyle Libre vs Dexcom G5 experiment

I started using the Dexcom G5 in May 2017. Since then the Freestyle Libre came out in Canada and has been growing rapidly in popularity. I was curious to try it to compare it with the Dexcom.

At a certain point I had double health insurance, which allowed me to make this experiment happen. I got the Freestyle Libre starter kit with the reader and two sensors and did two test sessions (a few months apart), where I wore both the Freestyle Libre and the Dexcom for 14 days. This gave me a good idea of the differences of the devices.

CGM vs FGM

If you are not familiar with the difference between a CGM and an FGM I will explain it briefly. 

Dexcom is a CGM which means it gives you a continuous feed of your blood sugar to your phone or Dexcom receiver. I use my smart phone with the xDrip app. The Dexcom alerts you if your blood sugar goes below or above a certain level, which gives you time to treat it early.

The Freestyle Libre is an FGM which also takes continuous readings but you need to use the reader to scan the sensor to get the results. It can hold 8 hours of data so you have to scan at least every 8 hours to see all the results. You can scan as many times as you want. The downside of this is that you don't get any alarms.

Design and insertion

The Freestyle Libre is a lot thinner than the Dexcom. I put it on the back of my arm as recommended and it didn't get in the way for me at all. I found the insertion easy and painless though the inserter is large and leaves you with a lot of plastic waste. I have to say I prefer the design of the Freestyle Libre sensor over the Dexcom, it simply looks sleeker. The warmup period (the time you have to wait until you can see some readings) is one hour compared to two hours for the Dexcom.

The Dexcom G5 insertion process is not as smooth as for the Freestyle Libre. It's more manual where you have to push the needle part (which is fairly big) in manually, then pull it back out. After that you put the transmitter in place and push it down. For the first few times after I got the Dexcom it felt a bit scary but I've been using it for a while now so I've gotten used to it. It does hurt a little sometimes but not always. I find it hurts a little more when I have the sensor on my abdomen than on my thigh.

The Dexcom is in two parts: a sensor and a transmitter while the Freestyle Libre is just a sensor. The Dexcom G6 does have a smoother insertion process that I look forward to trying once it becomes available here in Canada.

I find the Dexcom is still small enough that it doesn't get in the way. I rotate it between my abdomen, thigh and occasionally the back of my arm, though I prefer wearing it on my abdomen.

Accuracy

One of the most important things about a CGM is accuracy. Of course you want the device to give you the most accurate numbers possible compared to a finger prick result. I have the Omnipod which has a built-in glucose meter that I used as a base point for comparison. Keep in mind that manufacturers say that each meter can have an error margin of up to 20%.

The first day that I wore the Freestyle Libre I could not rely on the numbers at all. It constantly said I was lower than I was. This is considered normal as your body is getting used to the device. After 24 hours the numbers started to get more accurate.

I do find the Dexcom to be more accurate on the first day. It does depend on the site though, when I wear it on my thigh it takes longer to become accurate than when I have it on my abdomen.

In general, the Freestyle Libre gave lower readings than my Omnipod finger prick results, especially for the first few days. The Dexcom readings were closer to the Omnipod results and more consistent. Sometimes the Dexcom gave a little higher readings than the Omnipod but the readings were consistently closer to the finger prick results.

Here you can see a graph of the difference between the devices (the left side numbers are the value of my blood sugar in mmol/l).

Comparison of devices

The graph below shows the difference between the devices and the finger prick readings. As you can see the Freestyle Libre was more frequently far off, sometimes by a whopping 3 mmol/l. It almost always showed a lower number than the other devices.

Difference from Omnipod reading

The Dexcom did show a bit higher numbers at times but it was not far off. I would say the Dexcom wins on accuracy. The numbers were very close to the finger prick readings most of the time, sometimes exactly the same number.

Wear time and removal

The Freestyle Libre was reasonably accurate for the 14 days of use, though it was bad the first day and a bit off on the last 1-2 days as well.

I used a fixtape to keep the Freestyle Libre more secure. Many people seem to have an issue with the adhesive coming off early, but a fixtape helps. It stayed on well for the 14 days and it actually was a bit hard to get the sensor itself off as it was quite stuck. I do have dry skin and don't do a lot of sports nor go in water a lot which might have helped.

The Dexcom was more accurate but had to be replaced earlier. Often after about 10-12 days the accuracy goes a bit off for me so that's when I put on a new sensor. 

I used an ExpressionMed tape to secure the Dexcom which kept it well secured the whole time.

When I first got the Dexcom and before I learned about tapes I had some issues making it stay on long enough. I find the tapes are necessary to keep it on securely, especially if you want to wear it for more than a week.

Conclusion

Both the Freestyle Libre and the Dexcom have their pros and cons but overall I do prefer the Dexcom. Mainly for two reasons: accuracy and alerts. I don't always feel my lows and the Dexcom alerts me at 4.5 mmol/l, which usually gives me enough time to prevent a low.

I also find it extremely convenient that I can connect the Dexcom to my smart watch so simply by looking at my watch I can see my blood sugar. If my blood sugar goes too high or too low the watch vibrates. I find this gives me the best possible control of my diabetes.

Cost and insurance coverage is of course a factor and the Freestyle Libre is a lot less expensive than the Dexcom. I am fortunate that my insurance covers the Dexcom.

Keep in mind that every person is different and body chemistry and hydration levels can have an effect of how each sensor works. I know some people have accurate numbers with the Dexcom a lot longer than I do while others might have more accurate readings with the Freestyle Libre. Same with the adhesive, some people can barely keep the sensor on while others might have a hard time getting it off. You have to find what's right for you.

The perfect device for me would be the Dexcom but the size and shape of the Libre.