As I posted in another thread, my Minimed crapped out on the weekend (infamous Button Error) and I had to go back to Lantus/Novolog MDI for a couple of days while waiting for a replacement. I’d kind of forgotten half what I knew about doing it the old way even though it’s only been a few years–I’d been on MDI so long it was like muscle memory on an instrument but if you don’t practice for two and a half years it fades. So I was exceedingly glad I now have a CGM to help out, which I didn’t have back in my MDI days, but I was still finger-sticking a lot, and to my surprise the CGM readings were consistently undershooting my fingerstick BG’s by 20-35 points. I’ve had the current sensor on for just over 7 days and up until my MDI adventure it has been a super-accurate one, so this was a marked difference. Last night I got the replacement pump and switched over to it. This a.m. fingerstick said 103 and CGM said… 103.
I knew I was going to be running high with Lantus but I can’t think why my CGM would care one way or the other. BG is BG, doesn’t matter what you’re using to control it, right? Or no? Anyone else have this experience, or a hypothesis as to what’s going on?
Most of the time my CGM, either my Dexcom receiver or the CGM on the T:Slim G4 can be up to 80% +/- off from my meter. It was that way when I was on the vial and syringe and has stayed that way on the pump. So I can’t say why it happened to you. But with me, it’s all the time. When my CGM and finger stick are in agreement, or close to it, I almost faint.
Did your calibration frequency change from your recent pre-MDI to MDI to post-MDI periods? If not, my sense is that this is a coincidence. The accuracy of my CGM does vary over the life of the sensor.
I can’t say that I’ve noticed a difference between the CGM readings on pump vs. MDI, but I have noticed that my CGM tends to err on the low side a lot more frequently lately - probably since the 505 update. My guess is that that might be intentional. The receiver on the Vibe using the old algorithm tends to be closer to the meter more frequently than the receiver is.
