In this article we compare blood vs. breath biomarkers for detecting ketosis.
What are the similarities and differences between blood and breath biomarkers:
While blood and breath typically do move in the same direction based on one's level of ketosis, their kinetics are not the same.
The reality is that there are factors, many of which no one understands yet (such as the effect of time between the last meal and readings) that affect blood and breath differently.