I use the Medtronic Minimed Insulin Pump 670G which is actually part of a “system” as it integrates with Medtronic’s Continuous Glucose Monitor (CGM), so my glucose level is displayed on the pump usually (as you can see in the many blog posts I’ve written about this pump), and the pump will make adjustments to the insulin dose based on the real time glucose value from the CGM.

The CGM contains two parts — a sensor and a transmitter. The sensor has to be replaced every 7 days. (Well, they’re intended to be replaced every 7 days. Some people do have success extending them.)

When starting a new sensor, there is a “warm-up” period which takes up to 2 hours.

Until recently, the warm up period would always take the full 2 hours. But recently, I’ve changed my behavior during the warm up period, and now sometimes the sensor is ready after just 1 hour! When do I do differently? I eat breakfast while it’s warming up!

I used to try not to eat during warm up because I was afraid that I’d miscalculate the insulin dose and I would end up with high or low blood glucose….

Now I’ve become comfortable with eating during sensor warm-up. I just eat a breakfast that I’ve eaten before and therefore one that I know the correct insulin dosage. I put my pump in manual mode during warm up and I bolus based on the carbohydrate count for the meal.

Eating breakfast means that my blood glucose is a bit higher generally. Like today it was 173 mg/dL when I got the “Calibrate now” message early!

Also, one thing to note is that it’s NOT a good idea to calibrate when your blood glucose is changing fast. For example, one day I ate fudge and then was not able to calibrate. I’m sure the fudge made my glucose spike up fast and the calibration failed because of that. However, food that’s well balanced with insulin will generate a slower curve, especially if the food has a low glycemic index and is absorbed slower. So, let me clarify about the timing of my experience. I am eating breakfast right when I enter the warm-up period, and then the sensor warm up is completing in about one hour after I eat this meal, at which point my glucose may be trending up or down but isn’t changing too quickly.

Marinate the Sensor

I also “marinate” the sensor, which means that I put the new sensor in the night before and let it soak in my body’s fluids over night, and then I start the new sensor in the morning. I came across this practice from reading about it in the Medtronic 670G and 770G Insulin Pump group on Facebook. I’ve found that this marinate sensor process makes the sensor more accurate on the first day.

Marinating is slightly inconvenient because I don’t take a shower while it’s marinating because I don’t think it’s waterproof without the transmitter attached. So I wait to shower until after I’ve started the new sensor. Marinating is also not a process documented in any official Medtronic documentation, and I suppose could shorten the life of the sensor, although I have not had issues with that.

Why does eating breakfast help speed up the sensor warm up time?

I don’t really know. I assume it’s either because a) my blood glucose is higher and therefore the ISIG number is higher so the algorithm completes faster OR b) there’s something with the curve of how blood glucose rises after a meal which causes the algorithm to complete faster…

I am really curious about this, if you have any thoughts here. Please leave a comment below.