Ketonix Value to PPM, a Handy Conversion Reference

Dear World,

Ketosis is a natural metabolic process that occurs when the body does not have enough glucose for energy. When you are in this state, stored fats are broken down for energy, resulting in a buildup of acids called Ketones within the body. Some sources sadly still refer this as a "disorder" or some dangerous state. Those sources confuse ketosis with ketoacidosis, which is a very different thing that is of concern only if you are diabetic.

There is much literature about this state, and I won't try to replicate it. In fact, I am not a fan of regurgitating knowledge that can be found in documents and books written by much more qualified sources. If you want to know more, I urge you to read Keto Clarity, by Jimmy Moore. This books is a great source of information to understand how Ketosis can be used at your own advantage for a healthier and happier life.

For the purpose of this post, let me just say that, unless your are diabetic, being and staying in ketosis with a low-fat, moderate-protein and high fat diet, is a good way for many people to eat very well and lose weight and be healthy. 

If you want to live the "keto lifestyle", you'll probably want to measure your ketosis level. Measuring is the only way to make sure you are eating right to stay in ketosis. In fact, if you exceed a certain amount of carbs or proteins -- amount that depends on the on the individual -- you'll get out of the ketosis state and switch from operating as a fat-burning machine to operating as a glucose-burning machine

You'll have some options regarding how to measure it. I found that the most cost-effective and relatively accurate way to do so is to purchase a device called Ketonix, which is a breathalyzer able to measure the amount of acetone in your breath. Other methods include Ketone blood monitors (accurate, but the testing strips are very expensive) or urine test strips (inexpensive, but not so accurate, especially after your body gets used to being in ketosis.)

Fig. 1 - Ketonix 2015
The issue with these different methods is that they measure ketosis with different units, and it can be confusing trying to correlate them. While blood tests and the urine test strips give you a measure in PPM (part per million), Ketonix gives you a result in terms of Ketonix Value, that is described in the user guide as follows:
The KETONIX Value is a sensor relative value and is a percentage. Our template Nutritional Ketosis range is 40 to 70. This is approximately 0.5 - 3.9 ppm of Breath Acetone.
While the Ketonix Value is a perfectly good (relative) way to know if you are in ketosis, and to get a sense for the intensity level of the ketosis, it is hard to translate it and compare the values to the literature that usually describes measures in terms of PPM.

Fig. 2 - Ketonix to PPM, data as published on the Ketonix user guide

The Ketonix manual gives us a graphical reference to correlate the two measures:

While this is a good reference, I really wanted to be able to do two things that this graph alone didn't give me out of the box:

  1. Track my Ketonix Value readings using a spreadsheet, and know immediately the approximate ketosis level in PPM.
  2. Have a complete 1:1 correlation table between Ketonix Values from 0 to 100 and PPM, without having to interpret the graph each and every time.

Yesterday I decided to resolve this issue and came up with a solution that I hope you'll find useful.

As you can see from the graph, the correlation between Ketonix Value and PPM follows an exponential curve.  My theory was that it should be possible to describe the relation with an equation in the form:
Where PPM is the measure in PPM, and KV is the Ketonix Value. To find the formula, I put the data as published by the manufacturer of Ketonix in a spreadsheet table:

Ketonix Value PPM Acetone

Applying a little bit of math, I found that the generic exponential equation matches the Ketonix Value curve very well when a=0.0347 and b=0.0679. The resulting formula is:
The equation approximates the conversion with great precision. In fact, if you plot the data published given in the Ketonix user guide, and the one generated with the formula, the two overlap almost perfectly.

The following graph shows both the values reported in the Ketonix manual, plotted next to the approximation plotted using the formula (left axis). Also, the graph shows the percentage of error (right axis) for each of the values along the curve. Note how the approximation is pretty good, especially in the area of interest, that is in the nutritional ketosis range. The two curves overlap almost perfectly and are indistinguishable in this version:

Fig. 3 - Exponential function approximation * error

Zooming on the nutritional ketosis range ( KV = 40-70, PPM = 0.5-3.0 ), you can appreciate how the error is between 2% and 5.5%, which is a good approximation given all the other variables and error tolerances. In this view, the two curves are close, but you can distinguish them.

Fig. 4 - Nutritional Ketosis range, exponential function approximation & error

Using this formula, I created the following handy table that allows for an easy conversion of the Ketonix Value into a PPM value:

Fig 5 - Ketonix Value to PPM table

For example, if your Ketonix Value is 83, you need to look at the cell at the intersection between column 8 and row 3. The cell says "9.7", which is the approximate equivalent PPM value.

Fig 6 - Ketonix Value to PPM table, an example of usage

The compact form of the chart makes it handy to print and use as a quick reference. I printed a small copy, and attached it to my Ketonix device for reference.

A PDF version of this chart can be downloaded here. Feel free to download it, use it and/or distribute it as you desire. If you do, please just make sure to provide attribution to me (Lorenzo Pasqualis) and a link to this blog post.