Dex learning

OK, I am still with my first sensor insert since yesterday. Just now the Dex showed a BG of 178. I did the two calibration BGs and they were 104 and 102. (one touch ultralink). As soon as I entered the two BGs, the Dex then showed my BG as being 111. (I know the dex shows a previous minutes ago BG).

But how/why could the Dex drop from 178 to 111 within 3 minutes? It did something like that this morning too when I did the calibration.
I have read that the Dex gets more accurate after the first day so I hope that is true. So far, it is at least 30 to 65 points off from the meter BG.
Thanks for any comments from those who have been there done that with the dex.

I, too, started the Dex, about 6 weeks ago. I find that the first 48 hours tend to be unstable, but it becomes more consistent as time continues. I tend to use my meter more frequently then.

I've been using Dexcom since March, and the MM CGMS before that.

On the first day, the Dex is 'learning' how to relate the signal it is measuring from the tissue, with what you enter as the blood sugar level from your meter. It needs to have many readings to 'learn' and correct itself as it tries to correlate the data. The Dex is not directly measuring Blood Glucose, so it can only approximate what it is, based on the calibration readings.

So when you entered the 2 BGs (104, 102), and the Dex then went from 178 to 111, it was the Dex 'correcting' itself, not trying to show that there was an actual BG drop. By the second day, the Dex has more data points to correlate the 'tissue' glucose with what is entered from the meter BG, and that's why it gets more accurate as the week goes on.

I find that in the first couple days, if the meter and dex numbers are far off, I'll do a second meter BG. If the 2 meter BGs are close, I'll enter into the Dex, even if it isn't asking for one. Dex Technical support suggested that if the numbers are more than 20% off, it's good to enter the calibration, but make sure the meter BG is really correct.

After entering the two calibrations, the Dexcom will make an adjustment. Sometimes the adjustments seem to make no sense. Example, the original reading is close to a fingerstick reading, but when I enter the similar fingerstick reading, Dexie changes to something farther away from where it origially was.
Sometimes it takes two days to get better readings. I very often got readings way off the meter BG, especially when it was out of the range of 85 to 120, or so. Now that I have switched the sensor to my thigh, instead of tummy area, my readings are more accurate. Now it is often very close, when in range of 85-120.

Suzan & Pat, I have seen that kind of statement before about needing to be in that narrow range. I guess I don't see how it helps to have a cgm if it only works well when you are in a normal or near normal range. The time you need it to work is when you are low or high. I know all the arguments--it is for trends only, etc.
Also, if it is not very accurate for 48 hours and then, as some say, it drops off again near the end of the sensor life, you really only have about half of the sensor life for it to be helpful. Expensive gadget!! And yes, I chose it and will try it for some months to see if I change my mind.

Good point about the meter check. Though I have never been one to have a bunch of meters. I have a small One Touch that I just loaned to someone so will have to try getting another or finding my last one of a couple years ago. But my 2 readings each calibration time have been either the same or within a couple of points of each other. So the meter is consistent with itself, though it could still be wrong.

Hi Nell,
Other than the first day, my Dex readings are pretty accurate, in all ranges, not within a narrow range. However, on average, I avoid rapid rise/falls in BG, and rarely see single or double up/down arrows, so I think that helps keep the Dex more in line with meter BG.

I think each person finds over time what works best for them, so your results may vary. Give it a few weeks/months to get accustomed to it, and see how different sensor locations may work better for you than others. The 2nd sensor I did gave really bad readings, but then I noticed I didn't have the transmitter fully snapped in.

I had used the MM CGMS for 3 years prior to Dex, and MM was MUCH less accurate for me, so the Dex was great by comparison.

I find that it is important to do the first calibration on a new sensor when my blood sugar is fairly stable and in the 90-120 range. Then, on subsequent calibrations, I try to only do them when my numbers aren't moving fast up or down. If it is asking for a calibration but I just ate something an hour ago or took a big insulin dose, I will ignore the calibration request and wait a few hours until my numbers have stabilized again.

I use it to protect against low blood sugar. It works well for me to see a fast drop and it works well to tell me that I am getting low enough to need to pay attention to what my sugar is doing. I don't try to use it to calculate doses of insulin. between the 20% the meter can be off an the additional whatever percent the calibration between the meter and the CGM could be, it just wouldn't work to dose off the CGM.

It has been months since I have had a low blood sugar that I needed help treating. I have had low blood sugar incidents, but the Dexcom always notifies me that the problem is coming with enough time to self treat. Before the Dexcom, I needed help several times a week with low episodes. Most of the time, I didn't even know they were happening until after the fact. Some of them were quite scary. I had to test my blood sugar every time I drove the car and every 15 min while driving to protect against lows.

Stick with it a few months and see how it goes. Once you get used to it, you will wonder how you ever lived with diabetes without it.

The hardest thing I had to get used to when I first started on Dexcom was to not keep trying to calibrate it to match the meter. If you calibrate it too often, it seems to get confused and not give very good numbers.

Also, just in case no one told you. You can't take any meds with tylenol in them. It will mess up the sensor. The sensor will go very high for three or four hours then go back to normal, but it is never right again after that, it doesn't fully recover. Something about the acetominifin reacting with the agent in on the sensor wire. I have killed a number of sensors by taking various meds that I didn't realize had it in it.

Also, I find that the second week on the sensor is more accurate than the first week.

I echo the thoughts of the others here. I've only been using the Dex about a month or a little more and for a good part of that time I've had a love/hate relationship with my Dex. Now I can't imagine living without it because of the information it gives me that I wouldn't have otherwise.

I agree with you that the inaccuracies are frustrating at times. I mistakenly thought that I wouldn't have to fingerstick nearly as much with a cgms. When I realized I was going to have to test more often because of it, I thought what's the point then.

What I now realize is the protection it gives from lows because of the alarms - it gives you a heads up to be aware you're dropping and you need to test - the knowledge it gives you about which foods spike your blood sugar readings after meals and for how long, the knowledge of what your levels are doing overnight - are you dropping low and then rebounding or dawn phenomenon. If I'm shopping and I'm slowly drifting lower and lower, I can stop and check to see if I might need a few carbs so I don't go low (this actually happened today). It's a tool that I wish I had long ago.

I do find that most of the time when my Dex freaks out, it's when my blood glucose levels are rising or dropping - it's almost like it gets confused. I'm learning to be patient with that flaw because of the good things it gives me.

Good luck and give it some time. I think you'll grow to like it.