Users engaged in very low carbohydrate ketogenic dieting should be aware of the possibility of obtaining elevated BrAC results based on their diet.

Methanol

Methanol may be present in elevated concentrations on a person’s breath after consuming large amounts of fruit \cite{Lindinger1997}, in alcoholics \cite{Wigmore2008,Jones1988}, or through accidental exposure due to the improper production of distilled spirits \cite{Kane1968,Paasma2007,Aghababaeian_2019}. There are two unfortunate cases reported in the literature where a breath alcohol analyzer mistook methanol for ethanol, delaying medical treatment, resulting in the subjects dying from methanol poisoning \cite{Jones1989}. Users should be aware of the potential, but the unlikely possibility of elevated BrAC results due to methanol.

Limitations

Vaporous ethanol reference material produced by breath simulators cannot account for the complex physiologic gas exchange taking place in the lungs and airways of live subjects \cite{Jones1990,Gullberg1990,Anderson2003,Lubkin1996,Wilson1986,Vosk2014}. The SD of measurements taken in vivo has been shown to be greater than the SD produced by breath simulators \cite{Gullberg1989}. Further research is needed to determine the measurement uncertainty for in vivo results.
The calibration longevity of the analyzers was not examined in this study. An important consideration for those wishing to use these instruments is that the device must be sent back to the manufacturer regularly for recalibration. Individuals or institutions using these instruments may need to keep several on hand while periodic recalibrations are performed. 
Users of these instruments should incorporate quality assurance practices to ensure the accuracy meets the requirements of the intended use  \cite{Dubowski1994}. The use of compressed ethanol-gas reference standards would be a convenient way to perform accuracy checks \cite{Dubowski1996-dw,Silverman1997-zs}. Further investigation with these analyzers using compressed ethanol-gas standards is needed, as the efficacy was not assessed in this study.

Conclusions

The breath alcohol analyzers examined in this study showed the ability to measure vaporous ethanol with confidence in the results, especially at concentrations \(\le\) 0.080 g/210L. At the 0.080 g/210L ethanol vapor concentration, the combined expanded measurement uncertainty was \(\le\) ± 0.013 g/210L at the 95% coverage interval for all instruments. The likelihood of false readings from potential interfering substances appears to be small but may be a concern for those engaged in ketogenic diets with elevated levels of isopropanol. More work needs to be conducted with these instruments in vivo to determine the measurement uncertainty for the results which include a biological component.