Hi Mike,
If I get a Hi BG using my Accu-Check insight, I make sure that my cannula isn't leaking from any part of it at all.
A quick check can be had by dabbing a kitchen towel on the cannula after a bolus to see if you can see a wet patch.
I now see that 50% of my Hi BG's are caused by mechanical problems with the cannulas. Its not much of a problem if you know what your looking for.
You need to know what your Hi BG responses are and react quickly (after a test of course).
Also if I catch the pipe leading to the cannula, this normally leads to cannula issues.