Renal threshold and ketones are two separate things.
When the blood glucose is too high, the kidney's can't filter the sugar out of the blood so the extra glucose "spills over" into the urine.....that's why unregulated diabetics urine is so sticky and sweet smelling (it's also why they're so prone to UTI's...bacteria love all that sugar in the urine)
Ketones are produced when the body starts to burn fat for energy because there's not enough insulin to process glucose into energy. Think of it like this.....The cells of the body need glucose to live, but on every cell, there's a tiny lock. The "key" to this lock is insulin. Without the right amount of "keys", the glucose can't get past the "lock" and into the cell so the body looks for other sources of energy....it burns fat. But burning fat produces ketone bodies which, if they get high enough, start to "poison" the body.