Medtronic Guardian 3 Sensor CGM

The Medtronic Guardian 3 Glucose Sensor (CGM)



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The Medtronic Minimed 670g Insulin Pump has an auto mode which will adjust the basal insulin rate automatically based on the glucose readings from the Guardian 3 Sensor.

Like other continuous glucose monitoring (CGM) sensors, it produces real time readings of your glucose level by using a sensor that goes right under the skin. The sensor is pictured above. There is an insertion device that inserts the gold wire under your skin and there is a transmitter that attaches to it, which sends the sensor glucose reading to the pump.

The Guardian 3 Sensor uses a super thin strip of gold that’s about 1/4 of an inch (pictured above). The raw value from that sensor is called the ISIG value. Through a calibration process, this is converted into a glucose reading.

CGMs are amazing technology. I think being able to see a graph is game changing. And having the insulin pump automatically change insulin dose creates what is called a hybrid closed loop system. It’s getting close to being an artificial pancreas type system. (Although the pancreas does more than just produce insulin, so there are limitations, for sure.)

This is what the Medtronic 670G insulin pump looks like during the warm up process.

The Warm up Process

A sensor lasts for 7 days. After 7 days, you have to replace it. A brand new sensor takes 2 hours to “Warm up” so it doesn’t work for the first 2 hours. (Additionally, the transmitter has to be charged, which takes at least 30 minutes, so realistically there’s about a 3 hour gap without readings.). After 2 hours, you have to calibrate it by checking your glucose and entering the value. If you try to calibrate it when your blood glucose is high, or when your blood glucose is rapidly changing, it may not calibrate correctly.

Therefore, I usually test my glucose during this warm up period and make any needed adjustments, and refrain from eating my next meal until after I’ve done the initial calibrating.

I once had a sensor refuse to work and I think it’s because I attempted to calibrate it after eating fudge… My glucose was at 266 and likely dropping or increasing rapidly.

Replacing the sensor has become a super quick and easy process. However, the first several times we did it, we watched the video that shows how to do it, and that was very helpful!

Tiny Wire Made out of Gold

The insertion device has a needle that places a super thin strip of gold under the skin. In my experience, this either doesn’t hurt at all, or is a very mild pain experience. Sometimes I do bleed when I insert a new sensor, but this doesn’t effect the efficacy of the sensor.

Apparently the immune system is the reason that these sensors can only stay in for a week at a time.

For the Guardian 3 sensor, I measured this tiny wire and it is only 1/4″. Once in, I can’t feel it. There is tape that goes over the sensor and transmitter to hold it in place for the full 7 days. I usually wear it on my arm, but abdomen is another common place for it. If you insert it on your arm, you likely will find it easier to have another person help you… My husband usually takes the needle out and applies the tape.

Insulin pump displays information about when the sensor was last calibrated, how long the sensor has left, and what the raw ISIG value is.

Awesome but pricey tech

Being able to see a GRAPH of my blood glucose has been GAME CHANGING! To be able to watch how food, insulin, and exercise all effect my blood glucose is what gave me the desire to have an insulin pump…

I am frugal and a cautious spender, so at first I just bought the Freestyle Libre which is called a “Flash Monitoring System.” It works similarly to a CGM, but costs much less. However, it can not be calibrated and can not be used with the Medtronic Insulin Pump.

I recommend checking what your insurance covers and buying based on your needs — you can always change tech later. Honestly, the experience of seeing my glucose on the Freestyle Libre is what drove my desire to get an insulin pump. And then because I wanted the insulin pump to work with my glucose sensor, I switched to the Guardian 3.

At this point, the cost of the insulin pump supplies (infusion sets) and sensors cost more than the insulin, but I don’t regret it — it should pay off for my health in the long run.

Guardian 3 Sensor with Transmitter, on my arm!

I wear my sensor on my arm. In the above photo, the sensor is the gray thing at the top. The thing with the “G” symbol on it is the transmitter. The transmitter is rechargeable and reusable!


Guardian 3 Sensor works well for me. Insertion is often pain-free. Accuracy varies from being within a few points of my blood glucose reading to being off by 10-20 points. It requires calibration 2-3x a day, so fingersticks are still a thing, but the trade off is that the insulin pump can automatically adjust basal levels and I expect to have a lower A1C because of this amazing system.

Except for during the 2 hour warm up period, the insulin pump continuously displays a graph of my blood glucose level, making adjustments easier to make!

Related Reading

Bottom Line

Seeing a GRAPH is way better than relying on fingerpricks! However, it may make you want an insulin pump, if you don’t already use one, since it’s way easier to make corrections.

The technology will evolve and I hope it will become more accessible to everyone!


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