red wineImagine this far-fetched hypothetical scenario where an overworked, sleep-deprived, and hypoglycemic post-call resident is driving home (unbelievable, huh?). During a brief moment of weakness, he drifts to the right, but rapidly corrects his driving trajectory. However, a highway patrolman, Officer Poelis, is sitting along the shoulder of the road and notices the momentary lapse in the driver’s control. Sirens blare and the resident stops his car. Given the circumstances, the resident’s erratic driving behavior probably resulted from his prolonged lack of food and sleep. Officer Poelis, however, suspects that alcohol is involved and asks the resident to take a breath test. To the resident’s shock and surprise, he tests positive for alcohol despite not having had any alcoholic beverages since the last Residents Night Out party two weeks earlier.

Although a seemingly stretched hypothetical scenario, it is not beyond the realm of possibility. A Swedish group recently published a case report of a 59 year-old non-drinker who was unable to start a motor vehicle equipped with an alcohol ignition interlock device. A second breath-alcohol test revealed a blood alcohol level of 0.01-0.02 g/dL. These results were shocking, considering the gentleman has remained abstinent from alcohol his entire life.

There is nevertheless a biochemical explanation for the false alcohol reading. In an attempt to lose weight, the patient was on a very low calorie diet (VLCD). People on such diets or prolonged fasting states depend on fat metabolism for energy. Three forms of ketone bodies (acetone, acetoacetate, beta-hydroxybutyrate) subsequently accumulate in the body. The acetone can be metabolized by the liver to form isopropanol. A drawback of the breath-alcohol analyzer is that it cannot differentiate isopropanol from ethanol (the form of alcohol found in liquor). Consequently, despite the lack of substance use, he was recorded to have had an elevated concentration of alcohol in his breath.

Fortunately, blood alcohol tests utilize gas chromatography, which generate more specific results. This method could be used to verify false positives, but I doubt we will see bulky gas chromatograms in squad cars anytime in the near future.

Since this is the first case report of its kind, it is still unclear whether prolonged fasting states relate to a false positive reading. Besides the obvious warning to not drink and drive, I would strongly discourage the use of this excuse if caught. It would be much easier and safer to just find a designated driver. In the case of a resident on q4 call, finding a willing volunteer may be more difficult to accomplish.

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