@schleima Are you restarting your sensors? It’s the only reasonable reason for such a big discrepancy that I can think of.
It’s completely normal for a restarted sensor to be off more than 100 pts. But you can make the calibration process easier on yourself. Remember, appropriate calibration rules still apply. You need to be well-hydrated, your BG trend needs to be flat and stable (don’t restart a sensor after a meal!), and you need to be in range. I try to be as close to 100 mg/dl as possible once the warmup is done, as I find it makes the discrepancy smaller and requires fewer steps to calibrate.
Once you meet those criteria, you have to make sure to make small steps. 30% different than what the Dexcom says is generally acceptable (that’s when their official rules say you should calibrate), and sometimes you can get away with 40%, but that’s pushing it. However, I never change it more than 40 mg/dl at a time. Big jumps confuse the G6, so you have to take baby steps.
The problem comes with the next calibration. You wait 20 minutes and re-test. If your fingerstick has gone UP, you cannot calibrate it with another smaller number. Dexcom, and the T:slim if you’re using it, will just give you an error… But my Xdrip gives a little more information. It will actually say “confused calibration”, because the lower calibration doesn’t make sense when the sensor data KNOWS your BG was going up, not down.
However, so long as you’re staying flat or even trending slightly down, you can get away with another 30-40% calibration.
If it’s comfortably close, I’ll let it go at that point until the next morning. Since my pump keeps me around 110 all night long, I can easily afford to be 30-40 mg/dl off throughout the night. That gives the Dexcom plenty of time to get used to the new calibrations and avoid the “calibrate loop of death”. Then in the morning, I’ll do one more fingerstick, and can calibrate the sensor to exactly right.
So, in your example where Dexcom says 230, but your fingerstick reads 100:. Calibrate to 190. (30% if 230 is 69, which is bigger than 40, so 40 is the biggest I would calibrate.). Wait 20 minutes and re-test. If your BG has risen to more than 100, do not calibrate again. If it’s 100 or lower, calibrate another 30-40% or 40 points lower than whatever current value the CGM reads. It will usually fall slightly lower than the 190 you initially calibrated it to. So if it says 180 now and your fingerstick reads 95, I would take off another 40 points and calibrate to 140. (180 * 30% is still bigger than 40.). Unfortunately, the initial 130 or discrepancy is bigger than I usually have to deal with, except for maybe on day 20 of a sensor, so the difference is still too great for my comfort. I would wait 20 minutes again to do a 3rd calibration for the day. Be sure not to rush the calibration, even when they tell you 15 minutes, the closer together you do them, the more likely they’ll get rejected. Same rules still apply, you have to be stable or falling. Do not enter a lower calibration if your fingerstick has actually gone up. Assuming you’re now at like 90 and the Dexcom is reading 130, you can now calibrate it to 99. (130 * 30% = 39). That’s close enough for me, and I’m going to bed at this point! (I do tend to restart sensors in the evening.). In the morning, I’ll do one more fingerstick and calibrate it to whatever the fingerstick says. It’s been long enough since the last calibration that the fine detail rules no longer apply.
If you’re NOT doing restarts, and getting results more than 100 mg/dl off, there’s a bigger problem going on and you’ll have to figure out what it is. This is not normal of the G6. Not hydrated enough? Sensor in too lean of an area? Drug interaction? Compression low? First day wonkiness and you’d benefit from pre-soaking your sensor before starting it?
If you go through the initial pain in the butt to avoid the calibration loop of death in the first place, then the calibrations will indeed stick and the sensor will behave beautifully until the end of its life.
If you do fall into the calibration loop of death, yes, you won’t have a sensor number to work off of. You’re going to have to proceed with very cautious steps. Even if the Dexcom isn’t showing you data, you should still have a good idea where it’s at. It’s going to be wherever you calibrated to, plus or minus and real time variations. Start writing the numbers down. I wouldn’t try to keep stepping it closer to true at this point. Your focus right then should be getting out of the calibration loop (which should be avoidable in the first place if you followed my earlier instructions).
You tested at 100 and Dex says 230. You tried to calibrate it to 150, and Dex through a calibration error. It is theoretically holdings onto 150, it’s just not displaying it because it’s confused. Write down both 100 and 150. In 20 minutes you test again and you’re at 110. Do NOT try and creep it any closer to 110. You increased 10, so Dex thinks it’s around 160 (150+10). Calibrate it at 160 now. Write down both 110 and 160. Hopefully it takes this calibration because it’s logical, but it might still reject it. Wait another 20 minutes and re-test. Now your fingerstick reads 105. You went down slightly, 5 pts. Dexcom thinks it’s at 155 now (160 - 5), so calibrate to 155. By this point, it’s getting consistent calibrations and should not be rejecting it anymore. If should finally show a data point, so you can resume the actual calibration procedure. I would wait at least an hour to proceed with actual calibration at this point, though, because it’s going to be even more sensitive than usual.
I’ve been restarting the G6 for about 2 years now, so I’ve got plenty of experience with big calibrations and the awful calibration loop of death. Take the time to calibrate slowly and cautiously to avoid the problem all together!