722 Accuracy

[birds_eye]

Just want to post a question about accuracy. Well how accurate are your MiniMed 722s? I have had mine for about 10 days now, and I am not at all satisfied with the results it has given me.

For example, my Sensor reads 4.8, and I will test and actually be as low as 2.8. Also when I'm high, it does not correspond within 2mmol with my actual tested reading. I have tested on two occasions though, that it has been on target, but it is not a frequent occurence. Any suggestions? Could I be doing something wrong?

Please share your experience with me... thanks

[JediSkipdogg]

The CGMS sensors have a 40 mg/dl (2.2 mmol) error allowance. That is why I won't be going with a CGMS anytime soon. They say when you get into the 200+ (11.1 mmol) that they can be as much as 40% off and that is allowed.

Minimed is selling the CGMS as a way to help diabetes by saying you can see what you are running and then double check and correct from there. The problem is they aren't even good for that. The only good part of a CGMS is to observe patterns. You can see if you are dropping low at night and the suddenly rising. But even then that may not be fully accurate.

Another thing to remember, is the sensors can have as much as a 15 minute delay. Interstitual fluid itself has an 8-10 minute delay. The CGMS unit only reads every 5 minutes, so if one is experiencing a rapid BG change, it could be delayed by 15 minutes.

Here is something I posted in another post as well once....

This image shows BG fluctuations going up and down. The dotted line up the center is where all the numbers should fall. As you can tell, the Minimed reads low (when going low) and high (when going high) on everything. Why? Nobody really knows. Looking at the Navigator CGMS, it is 100% the opposite. The key point, is the Navigator is showing what it should. In a CGMS unit, they read interstitual fluid. That means that there is about a 6-10 minute delay from what your BG reading is. That means if you are increasing in your BG, the CGMS unit should always be lower, as it would be your BG rate 6-10 minutes ago. The Minimed reading high on a rate going up has absolutely no theory behind it.

http://img232.imageshack.us/img232/8819/zdc010054964001b7mk.jpg

The following image has multiple problems with it in my opinion. The first one being the Minimed CGMS is reading high and won't go below 65. In fact, the Minimed CGMS WILL NOT read below 50 at all. But if at 50, a CGMS is reading 70, that's 20 points off. That means at 70, one would be 90, and 90 is a great reading. That can be very misleading to people on decisions they make for exercise, driving, etc.

The Navigator CGMS actually seems to stay on the results pretty well and then adds the delayed effect when the BG starts to rise rapidly.

http://img65.imageshack.us/img65/7026/zdc01005496400020ib.jpg

And then for those uber nerds out there...the following is a rate error grid showing the accuracy of these units compared with reference BG (lab tests.)

http://img137.imageshack.us/img137/3936/zdc010054964001a9te.jpg

[Funnygrl]

So moral of the story is- hold out for the navigator?

[JediSkipdogg]

So moral of the story is- hold out for the navigator?

Yup, and if that's not as promising at is seems to be...then hold out for the next phase of CGMS units. I'm not trying to persuade anyone from going on a CGMS, I'm just trying to put the facts forward now so they don't spend the money and then find out there's no refund once used. That and the CGMS makers aren't being up front with some questions. If you ask them about accuracy they will tell you that they are pretty darn, but won't tell you that it's only 40 mg/dl accurate and only 40% in the higher range.

Oh yeah, and the calibration of a CGMS is only as accurate as your BG meter. So say you test with your BG for a calibration and you are running by lab test of 100 mg/dl, but your meter reads you at 110 during that same test and you calibrate by the 110. Well, you just put your CGMS reading higher than normal and then it has the 40 mg/dl window. So you now have a very high innacuracy rate.

[Dewey]

Really, birdseye, it's up to you whether or not to go with it (or wait). Different people have different perspectives, so what may help one, may or may not work for another.

I haven't really heard too much either way in terms of accuracy on the 722 (I did hear from one friend that hers was acting up lately :s: ), but when I trialed the CGMS system, it did pretty well overall (despite the fact we had to insert the sensor twice).

One thing I wanted to mention, is that my doctor informed me that these systems aren't so much for or about accuracy, they're used more commonly to track trends in levels. In addition, they can aid in trying to catch & treat a rise or decrease in sugar levels sooner. Just another thought to keep in mind.

[nshack]

Yep, whether accurate or not, the sensor will show rapid rises or drops in b.g.. If you get the double arrow either up or down, it's tracking a rapid change. You should then be alerted enough to start checking your glucose with a meter and head it off before it gets out of hand.

I'm not crazy about them, but a study showed that people using them to track trends and head off highs were able to lower their a1c in a week using it.

[Tim_Roy]

Yeah, my nameless NPA told me "off the record" that he wasn't at all enthused about the 722's sensors' accuracy. But yeah, these things are basically good for tracking trends.

I had an option to get a Dexcom on the cheap, I declined as it's actually cheaper for me to borrow their's and just pay for the sensors once or twice a year to get my control mechanisms mastered. Had I not used the Dexcom I don't think we'd have ever figured out that my digestion had slowed and I needed to be on (almost) all square wave boluses.

[Vic L]

ok, I have a 722 but not the CGMS sensor. I love the pump and its functions. The added function for active insulin has helped my BGs tremendously.

Vic L

[nshack]

Yep, I am on the 522 without the cgms and I like the smart features that give you a leg up on all the data. I keep finding more when I poke around. It's pretty cool. Even when I am low, I use the bolus wizard to see how much active insulin is still threatening so I can accurately address the hypo, and only once. It works. It'll say correction: -0.4 units. So Iknow that I'm going to need to consider that when I take glucose.