I'm surprised that it's taken you DSN 5 years to tell you about DKA, how to check and hopefully how to combat it...
And if you were very poorly etc when you were first DX'd then it's probably you were suffering from DKA...
Simple measures such a maitaining good control and reacting quickly with implement sick day rules will help to prevent going into full blown DKA... Once experienced once you are in no rush to experience for a second time..
If you Bg hits 14mmol/l then check for ketones, if you find none then do your normal correction procedure.. How ever if you find some, doesn't matter whether it's on a trace you need to be taking some measure to combat them..
Which is many drink plenty of fluid to keep yourself hydrated and flush out the ketones, with a correction dose to lower you BG, recheck state of play at two hours BG and ketones... Repeat a correction dose if still high.. And you basically keep checking every two hours until they flushed out, if you find your BG is normal but still have traces of ketones, then re check after an hour to ensure that BG's aren't going to go back up..
Problem is with ketones is that we all have different tollerance levels to when they start to kick in, some diaebtic find they start getting them at 14mol/l others will have a much higher tollerance level..
I haven't had DKA since I spent most of my pregnancy in and out of hospital with it several weeks stay at a time, that was 20 years ago and since then I've had a couple of bouts of norvacs virus, flu and Glandler Fever apart from having to implement sick day rules to prevent my BG rocketing out of control, I didn't have any signs of ketones phew. But I will always check and monitor if for any reason my BG hits over 14mmol/l