Urine ketones don't have much to say about fat adaptation. There's an old study that looked at extended fasting--weeks with no food. They experimented with small amounts of glucose, eight to fifteen grams. Urine ketones disappeared, but blood ketones stayed at the same high level. In an extended fast, about half of glucose production is from the kidneys, this produces ammonia, very alkaline, the authors suggested the ketones were spilled in the urine to lower the ph. The little bit of glucose resulted in a decrease in ammonia production, so those ketones didn't need to be spilled.