Bad Sensors: Yes, and I think that Dexcom has phone-called ALL customers who ordered Sensors during the period of bad manufacturing lots. (I got a “cold call” on the phone from them 3 days ago.)
After a few days, you’ll catch on to the fact that the trend is really of more value than the numbers. Even though the data is 10-30 minutes “old”, the shape of the graph is a good indication of where your bG is going in the near future, and you can adjust (in advance) for dosage problems and suprises which are barely getting started, and haven’t completely happened yet.
None of us had such a graph before getting CGMS devices. Even if you DID take enough bG readings, you’d only a set of numbers. (And at a mere 20x per day, I never did enough tests to get a quality graph anyway.) Until you’re poking at least every 10 minutes, AND you graph them on paper, or on the screen, you don’t get a good feel for the 2nd-order shape. (The high school calculus “derivative” of the curve.)
Alarms are great when you’re sleeping or too busy to poke, but the shape of the graph is a totally new tool for us PWD’s. You get to see “roller coaster” events starting to happen, and you can deal with them before they reach extreme values of bG.
Dexcom has a tendency (seen by really finicky people who study it closely), to be more prompt during falling bG, and much “later” when trying to catch up with increasing bG. Basically, falling Glucose levels happen locally at body cells and ISF first, while bG falling in your big volume of body blood happens as an almost secondary effect.
So, during falling bG, Dexcom’s delay across the membrane and into Glucose Oxidase is partly a “tie” for the delay of seeing the bad news in fingerstick bG. So this creates ‘Good News’: For some people, in many situations, Dexcom is sometimes just 0-5 minutes “late” compared to blood bG. Bad news: Both values are late, your cells were suffering from low glucose supply before either measurement fully indicates the problem. (I’m sure that you’ve often FELT signs of “going low” before finger stick shows the fall, it happens to all of us. This is why.)
But, on the “going up from uncovered food” direction, Dexcom is very late. Whether obtained from the stomach, or directly at the mouth, or the small intestine, or liver converting non-glucose compounds into glucose, the blood gets it first. The delay from blood to ISF is additive with the delay from ISF into the Dexcom’s glucose oxidase.
I don’t know why Minimed Sensors doesn’t show a similar “more prompt when falling” behavior, but if it’s there, it seems to be much less.