After starting to use the ketonix I began wondering how the ketonix readings might relate to total blood ketone levels rather than just to breath acetone (which is the only correlation provided in the ketonix manual) and what a ketonix reading of 100 would mean if such a reading could be obtained.

I didn't manage to find an existing correlation between the ketonix and blood ketones but for what it is worth I have derived one myself using two correlations from the literature for breath acetone vs plasma acetoacetate (AcAc) and for breath acetone vs plasma beta-hydroxybutyrate (b-HBA)– see Figures 3 & 4 in the following reference
"Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals" http://ajcn.nutrition.org/content/76/1/65.full

I will spare everyone the mathematics but the procedure I have used is as follows:
1. Convert the ketonix reading (0 to 100) to breath acetone in ppm.
2. Convert the estimated breath acetone in ppm to units of nano-mol/liter
3. Estimate plasma AcAc and plasma b-HBA in mmol/liter from the correlations
4. Add AcAc and b-HBA to get an estimate of total blood ketones in mmol/liter

The results of these calculations are shown in the following chart:


For additional interest I have included in the above chart the blood ketone level thresholds for the start of nutritional ketosis, optimal ketosis and starvation ketosis as per the following Volek and Phinney chart from chapter 10 of their book “The Art & Science of Low Carbohydrate Performance”:

Looks like a ketonix reading of 100 would correspond roughly with the onset of starvation.