MENS REA: Measuring nothing

By Mike Nichols

The fairness of Michigan Law that "any presence" of a schedule 1 controlled substance in the blood stream merits scrutiny.

The phrases "100% certain," or "absolutely positive" are phrases that may have a place in advocacy but have no place in science because they are not couched in data. A scientist who conducts a scientific analysis may be able to say "based on the data, I can say within a reasonable degree of scientific certainty that...." A scientist would not and should not say "I am 100% certain that what was analyzed is marijuana because our data looks very good."

Michigan's "zero tolerance" or "strict liability" law for driving with "any amount" of a schedule 1 controlled substance in the driver's blood is based on the assumption that a crime lab can distinguish between "zero amount" and "any amount" of the drug being tested. (MCL 257.625(8))

This assumption is flawed. The Michigan State Police forensic science division lab uses thermal-fisher gas chromatograph/mass spectrometer systems. The sound of that name may boggle your mind. It is not as complicated as it seems.

The gas chromatograph separates the compounds in a gaseous mix. The chromatograph is "taught" what time each compound separates from the mix when the analyst injects a mix with that compound into the chromatograph then observes the time it takes to separate. When a gas compound is injected with unknown compounds, the time that each component separates from the mix is analyzed. That is how the gas chromatograph identifies each component in the mix by separation.

After the gas chromatograph separates the compound, the compound is injected into a mass spectrometer. The mass spectrometer breaks off an electron and identifies the molecular structure. If the unique molecular structure is matched to the molecular structure for the compound of interest, then the analyst can identify the compound such as THC. Think of it like identifying points on a fingerprint. The Michigan State Police lab uses 12 "points" in its THC analysis 4 for THC, 4 for duterated THC metabolite and 4 for the THC metabolite.

The problem with the assumption that the instruments and method can measure nothing is simply that there is always something there. One of the leading manufacturers of gas chromatographs/mass spectrometers is Agilent Technologies. A Technical Note published by the Chemical Analysis Group of Agilent recommends statistical methodology to determine the signal-to-noise ratio.

The signal-to-noise ratio allows the analyst to understand the lowest quantity of a substance that can be distinguished from the system noise if the substance is absent from the sample (Wells, Prest and Russ, p 1). This limit is known as the "limit of detection."

A number of factors contribute to the limit of detection and several types of limits also need to be considered including the instrument detection limit, the method detection limit, the practical quantification limit and the limit of quantification.

The Michigan State Police (MSP) administratively established its limit of detection at 0.05 ng/mL of THC and its limit of quantification at 1 ng/mL of THC. To give you some perspective, 1 nanogram per milliliter equates to a 1/2 teaspoon of sugar distributed in an Olympic sized pool. The limit of quantification is the cutoff level below which the MSP will not report it detected THC in a blood sample.

The MSP has never produced a study that demonstrates the validity of the cut-off level. Ten years ago former lab toxicologist Michelle Glinn analyzed some data on detection limits. Her replacement, toxicology unit chief Geoff French, studied the data. He does not agree with Glinn's methodology. In part, French says because Glinn used case results in the database and assumed that those results were accurate.

French also testified that the MSP is analyzing the current limit of quantitation or "cut-off" level and may increase it in the future. That news is certainly welcomed but it begs the question about the current language of MCL 257.625(8). The statute prohibits a person from operating a motor vehicle with "any amount" of a substance listed under schedule 1 of section 7212 of the Public Health Code. Those substances include marijuana. So, how does a person acquit himself of a charge under (8) of MCL 257.625 if all the state has to prove is an amount of THC in the blood that equates to a 1/2 teaspoon of sugar in an Olympic size pool--especially if it is scientifically impossible to measure nothing? The courts are now confronting these issues. Hopefully, science will have a hand in the equation.


Mike Nichols is a sustaining member of the National College for DUI Defense, the delegate for Michigan to the college and author of the "Michigan OWI Handbook" by West and co-authored "DUI Mathematics" for the Inside the Minds Series by Aspatore Publishing. He is also an adjunct professor of DUI Law and Practice at Thomas M. Cooley Law School's Lansing campus. mnichols

Published: Fri, Aug 31, 2012