In my experience, the lack of a trend arrow occurs when my CGM is bouncing around and having trouble giving accurate readings — usually at the beginning or end of a sensor session.
Does your CGM seem to be working well?
Has the problem persisted? Often the CGM soothes out on its own (especially if the problems are in the first 24 hours of a new sensor.)
You didn’t do anything wrong. The pump is forcing you to be more active in the dosing decisions because the CGM data is unreliable. Dexcom doesn’t display a trend error when there are statistical errors in the data, I.e. it’s too jumpy. You may not even see the jumpiness, since Dexcom uses a smoothing algorithm to display pretty and meaningful graphs, but the lack of trend arrow is telling you the system has no confidence in the data it’s displaying. The formal literature says you have to fingerstick for dosing decisions when there’s no trend arrow. And you’re right, you shouldn’t have to!
You can change the sensor and make Dexcom send you a replacement. You may have to fudge the form a little since they don’t have “this sensor isn’t good enough for my pump automation to work flawlessly” as a failure option". Personally, I would pick whateber the option for inaccurate readings is tell them whatever they want to hear the the follow-up questions. Or you know, your food to to stick it out and hope the sensor settles down. Maybe drink some water…
Sounds like a Dexcom problem and not a Tandem problem. When my CGM is working well and data is coming in normally, it will populate automatically with my blood sugar. If my line is all wonky for whatever reason, the pump doesn’t use that information to calculate a bolus because it doesn’t know if it will need to add more insulin or take some away etc.