That is a good question. I will do a more extensive article on the ketone bodies soon (acetone, acetoacetone, and beta-hydroxybutyrate (B-OHB)). For now, lets focus on acetone (what the Ketonix measures, blood testers test BHB). Here is a little summary of the process.
Acetoacetone and beta-hydroxybutyrate (B-OHB) live in reversible equilibrium. They can be converted back and forth between each other as needed. Acetone is what is called a terminal pathway. Once it is created (from acetoacetone) you can’t go back. It is a waste product excreted through breath or urine.
All that being said, there is a fair correlation of the breath analyzer with blood ketones in many situations (some situations they can deviate). It shows that the process of converting acetoacetone is active (thus producing the waste product acetone). Here is an example of testing breath and blood meters:
So if you are showing some ketones in the morning, it is a good bet you are in ketosis all day if you are eating a well formulated ketogenic diet.