False lows with Dexcom?

[7kmom]

After playing the "how low can she go" game 2x yesterday and nearly all morning this morning...
Dexi is still saying she's only in the 50's. Her pump meter says she's (finally) up to 129, so i thought to recalibrate the Dex because it asked to be calibrated earlier today when she was so low.

And low and behold the dex and the one touch ultra are still saying she's under 60.
sigh.
I'd like to use the cgm technology. Until yesterday it was pretty good. Yesterday was the first day with the new (replacement ) reciever and a new sensor. During yesterday's game it was pretty close to her pump meter, registering low and quite low numbers just as her pump meter was and the way she was feeling. All pretty much agreed.

Could it be the sensor is malfunctioning? Maybe i need to make a call to tech support?

Any other ideas?
thanks,
Carol

[BrendaK]

My mom got false lows all the time with Dexcom, especially at night. Her meter would say 90, Dexcom would say 40. She ended up returning the Dexcom because it kept (false) alarming her all night long. It wasn't malfunctioning, it just isn't 100% accurate.

[rickst29]

one of the most accurate of all meters. If your "pump meter" disagrees and it's a Cozmo, you probably have damaged strips. (Cozmo's built-in Abbott Freestyle is also very good.) But if your meter is Minimed, with the old "BD" meter, I wouldn't trust it.

Solve the bG meter discrepancy first: Try a FRESH bottle of strips, and also test using the same blood drop, from the current bottle. (It only takes a few seconds to move the calibration code to match the alternate bottle, the blood is still fresh enough to use.) If you can, also try with a completely different One-Touch meter too-- using the same blood drop. (I have 3 OTU meters and two calibration cables, to assure that I always have an extra in case of losing one.)

Even if your "pump meter" is a Freestyle, it should be re-verified the same way. (Current strips versus a fresh bottle, preferrably from a different lot number.) It's smart to also use fresh batteries before doing anything else, they cost almost nothing.

If the calibration bG meter is presenting bad data, then of course the Dexcom will present bad data too. And if you're believing the 'BD' meter on a Minimed when they give conflicting readings, well, I wouldn't do that!

[Kaylee's Mommy]

also need to remember that the cgms are typically behind.. K's minilink will keep alarming after she's come up.. until it catches up in a few minutes.. we did have a bad sensor.. it was the end.. on day 9.. and it just didn't have the ummph the others had.. I KNEW it was bad.. she was below 100 all day, but it would rise with her bg just wasn't where she was suppose to be.. and then fall.. so I KNEW it was off, but it was giving me a pattern.. when I got the change I changed it out..

[Jeff]

It's very important to be aware of the different compartments being measured as you discuss CGM and blood.

Blood glucose meters measure glucose levels in whole blood.

Continuous sensors measure glucose levels in interstitial fluid.

These are very different biological fluids and the glucose levels in the two are in constant flux. Glucose is delivered first to the blood, then to the intersititial space. There is some time delay in this glucose delivery, and while various people quote various numbers of minutes the important take away as that this delay is not zero. Glucose changes tend to lead in the blood.

So when people say "my sensor is not accurate because it doesn't match my meter," I worry that they do not fully understand that these devices are measuring different things and that one should not expect them to be the same except under specific circumstances -- and those circumstances are when your blood glucose levels are not changing and you have calibrated the sensor as designed (i.e., during periods of little or no glucose change).

Some years ago a group from Scandanavia reported on a study in pot bellied pigs which showed that the glucose levels in the brain correlated better with interstitial fluid than they did with capillary blood. When you think about what you really care about, it's the glucose level in your brain, not your finger, so sensor data may end up being as important, if not more important, than blood data. For that to happen, sensor precision has to be as good as blood glucose meter precision (low error compared with laboratory standard) and we have to learn how to use the sensor data to dose insulin and correct for impending lows. That will take time, but I believe that we will get there.

[7kmom]

Thanks for posting as well Jeff.
I try to remember that Intersticial fluid runs behind BG. But when sometimes they are right on, it's hard.

I was just surprised that there was such a descrepancy that time.
Usually, if Dexi doesn't register the fix nearly immediately, (because i've noticed sometimes it does within the next reading, ) I try to leave it alone, knowing it will come back soon enough.

Still new to this, and she has a cold so we are still playing limbo a bit.
Kind of nice having Dexi around though.
Just have to remember to trust the direction it says she is going.
thanks.