Sunlight and the Dex G4: A Bad Mix

Laddie_Head SquareI’ll start this post by saying that I am very happy with my Dexcom G4.  It is by far the most accurate of the CGMs that I have used, the previous two being the Medtronic Sof-Sensor and the Dexcom 7+.

But I think that it has one serious problem and I am surprised at how little I have seen written about it.

The G4 has a beautiful color screen and uses yellow for highs, white for in-range readings, and red for lows.  When I hike in Arizona and am in bright sunlight with little or no access to shade, I cannot read anything on my Dexcom that is in red.  I can see the white numbers the best and can vaguely see the yellow numbers.  But even when I put my receiver in the skimpy shade of a desert bush and use my hand to shield the receiver as much as I can, I cannot see the red numbers or read the red low alert screen.  My glasses have transition lenses which turn dark in the sun, but I think that it is a reasonable expectation that people spending time outside will be wearing sunglasses.

So when I am hiking with my G4, how do I know that I am low?  I can see the white numbers fairly well and the yellow numbers a little less well.  So if I can’t see the number at all, then I must be low!  I don’t think that is exactly how the CGM is supposed to work…

Dex and SunWhen my Dex alerts me to a low, I know I need to test and take action.  My alert threshold is set at 70.  Does the current alert mean my BG is 69 and a glucose tab or two will take care of the problem?  Or is it 49 and I’m in danger of falling off a cliff?  I can’t answer that question because I can’t read the number.  When I’ve been in bright light for a long time, it is also difficult to see the directional arrows to know if my BG is dropping, stable, or rising.

I’m sure the idea of using red for lows was thought to be a good one because red is often associated with danger and emergencies.  Unfortunately testing of the screen readability must have taken place in a lab not out in harsh sunny conditions.  I wrote a long email to Dexcom about this problem and never received a response.  I will call them soon just to get the problem on record.  I can see things on my iPhone screen in the sun, including red text, so a fix of this issue is not an insurmountable problem.  An easier fix might be to stop using red for any of the vital information.

There is a December 2012 thread in the TuDiabetes Dexcom Users group about this issue and I bumped it up on Monday to see if others ran into the problem this summer and there are a few new responses.  The original author of the thread was a cyclist who couldn’t see her G4 numbers and arrows without getting off the bike and moving into the shade.  As she said, this wasn’t a good option for races.

Is anyone else having this problem?  Any suggestions or solutions?