"Good" vs. "Bad" Calibrations

I've read quite a few opinions about optimal times to calibrate a Dexcom and particular times when one should not calibrate their Dexcom.

I've attempted to collate these opinions to the best of my ability, and what I've come up with is the following:

Good times to calibrate:
*when the directional arrow is horizontal (i.e. no upward or downward trend)
*at least 30 minutes before eating or at least 30 minutes after eating
*at least 30 minutes before or 30 minutes after any insulin is administered
*at least 15 minutes after a prior calibration (with the exception of the two required readings after starting (or restarting) a sensor

Bad times to calibrate:
*when BG is higher than 220
*when BG is lower than 70
*more frequently than 6 times daily

Based on your own experiences and/or what you've read here on tudiabetes or elsewhere, please comment on the accuracy of what I've outlined above. Also, links to any reliable sources touching on this subject will be greatly appreciated.

Thank you in advance.

ETA: What do you do when you accidentally enter an incorrect BG when calibrating? Do you immediately enter the correct reading or do you wait?

Your good/bad times look perfect to me.

My Dex trainer told me calibrating twice daily was best — and it didn't have to be exactly 12 hours apart. When I asked if calibrating more than that was helpful, she said no, it was not, EXCEPT for the first 24 hours, then it was helpful.

Hope that helps!

I've never found a bad time to calibrate. If I'm concerned about a particular calibration, I'll just do it again in an hour or so. Calibration is a measurement of movement just as it is anything, so not calibrating is much worse than calibrating badly.

I'd like to add the following to my original post (in actuality, it should replace my original post):

I've heard a lot of anecdotal evidence surrounding optimal times to calibrate, how often to calibrate, and when not to calibrate your Dexcom. A lot of the information I came across was conflictual, so I called Dexcom and was connected with one of their CDEs who, IMO, sounded like she knew what she was talking about; she did not sound like she was reading from a pre-scripted "Answers to FAQ" sheet. Following is a summary of the information she gave me. I make no guarantees regarding the accuracy of this information, so proceed with caution and with the knowledge that YDMV.

A. This is when you should calibrate:

1. When you are prompted to calibrate by either:
a. Two red blood drops that appear two hours after starting (or restarting) a sensor OR
b. One red blood drop (these prompts occur every 12 hours)
Caveat: Do not calibrate even if prompted to do so by a blood drop if the trend arrow is pointing either straight upwards or straight downwards (one or more arrows). If this is the case, WAIT until the directional arrow is either horizontal, trending slightly upward, or trending slightly downward before calibrating. Be patient; you will not be "timed out" if you do not calibrate immediately after a blood drop icon appears.

2. Whenever a meter reading is greater than or equal to 80 mg/dL AND the Dexcom reading is greater than 20% higher than the meter reading or more than 20% lower than the meter reading.

3. Whenever a meter reading is less than or equal to 79 mg/dL AND the Dexcom reading is more than 20 mg/dL (not 20%) higher than the meter reading or more than 20 mg/dL (not 20%) lower than the meter reading.

B. This is when you should not calibrate:

1. If BG (via meter) is higher than 400mg/dL.

2. If BG (via meter) is lower than 40 mg/dL.

3. If any of the following appear on the Dexcom screen:
a. question marks
b. an hourglass
c. the antenna icon (receiver is out of range of transmitter)
d. one or more trend arrows that point either straight up or straight down (horizontal arrow or arrows trending slightly upwards or slightly downwards are O.K.)
e. no trend arrow(s)

REMEMBER: More is NOT better when it comes to calibrating the Dexcom. Calibrating more often than when instructed to do so by blood drop icons or when the Dexcom reading is not inaccurate ("inaccurate" as defined by A.2. and A.3. above) will not improve the accuracy of your Dexcom and will likely worsen the accuracy of your Dexcom readings.

Some, but not all, of this information is available on the Dexcom website: http://www.dexcom.com/sites/dexcom.c...ney/story.html