I never tested for blood ketones until about 4 years ago when I mentioned to my diabetes consultant that I'd never had a DKA and didn't test for ketones. She promptly gave me a testing meter that checks for ketones and I have a repeat prescription for 1 box of 10 strips a month (might be every 3 months).
Now I use them if I am feeling queasy/ill and/or my bg is persistently high. (Still haven't ever managed a level higher than 1.6, when I was ill?) My (possibly incorrect) understanding that anything under 0.6 is perfectly normal for someone not on a keto diet.