Ketones are produced when fat is broken down, so strict low carb dieters often test for ketones just to check the diet is working and they are losing fat.
In diabetics, ketones are also produced when fat is broken down. However if this happens because the system is short of insulin, it can be dangerous.
Thus ketones with low/normal bg are harmless, but with high BG can be a warning that ketoacidosis, a potentially fatal condition, is beginning.
That means that consistent high sugars with ketones are a BAD THING Low sugar and ketones is NO WORRY
In addition, The ketones in your urine will have been accumulating all the time since you last emptied your bladder, which could be several hours. That can't give you an early warning.
the advice to check for ketones after 3 high BG readings makes sense.
SO to sum up. Ketones +low BG~ don't worry
Ketones + high BG ~ get to A&E
Hana