Breath and blood ketones both change, often dramatically over the course of a day. The patterns of ketone level changes are dependent upon the specific day and the individual.
Although breath and blood ketones tend to rise and fall together (graph a.), there is often a time offset between changes in blood ketones and changes in breath ketones (graphs b. and c.) For this reason, the correlation between coincident blood and breath measurements in our study and in the literature (Refs. 1-3) appears moderate (R2 ~ 0.6).
Because ketone levels often vary greatly throughout the day, a single ketone measurement provides a limited view of an individual’s metabolic state. In order to capture cumulative progress over time, we capture cumulative progress over time, we calculate a daily area under the curve (AUC), or Ketone Score.
The Ketone Score is represented by the colored area in the BIOSENSE™ app. The AUC or Ketone Score is a summary of the accumulated depth and duration of nutritional ketosis each day. It answers the question, “how deeply and for how long have I been in ketosis?” with a single number.
Our clinical data showed a very high correlation between breath and blood AUCs (R2 = 0.83). Stated differently, using a breath or a blood device to take multiple measurements per day, which is necessary to capture the high variability of daily ketone levels, provides very similar indications of overall ketone activity.