Alcohol Testing: Non-Alcoholic Causes of Blood Alcohol Levels - Family Medicine

Dr. Cai Jueren reply Family Medicine

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Hello: I would like to respond to you using a report from Professor Chang Wei-tun of the Department of Forensic Science at Central Police University and Secretary-General of the Chinese Forensic Science Society.
Alcohol suppresses the central nervous system, causing visual and auditory impairments, and reduces attention and judgment.
The degree of its effects is proportional to the concentration of alcohol in the organism.
After consuming alcoholic beverages, approximately 20% of the alcohol is absorbed by the stomach, while 80% is absorbed by the small and large intestines, distributing into the bloodstream within minutes.
Through the catalytic metabolism by liver dehydrogenase, about 95% of the alcohol is first converted into acetaldehyde, then oxidized to acetic acid, and finally oxidized to carbon dioxide and water.
The remaining approximately 5% is excreted through feces, urine, breath, skin sweat, and saliva.
To measure the residual alcohol in the human body, tests can be conducted using blood, urine, saliva, and breath; however, due to the difficulty of collecting blood, urine, sweat, and saliva samples for law enforcement, a more feasible method is to convert breath alcohol concentration (BrAC) to blood alcohol concentration (BAC) for testing.
The principle of measuring breath alcohol concentration is based on Henry's Law, which states that the solubility of a gas in a liquid is proportional to the partial pressure of the gas in the vapor phase.
Therefore, under constant temperature and pressure, there is a specific ratio between the alcohol concentration in the blood and the alcohol concentration in the exhaled air.
Currently, the accepted ratio of BAC to BrAC is 2100:1; in other words, the alcohol content in 2100 milliliters of exhaled air is approximately equal to that in 1 milliliter of blood.
There are three categories of methods for testing breath alcohol concentration.
The first category is based on physical principles and can be divided into "infrared absorption spectroscopy" and "conductivity methods." The former utilizes the fact that alcohol absorbs specific wavelengths of infrared light for qualitative and quantitative analysis.
Additionally, to prevent various potential interfering substances in the breath from causing an increase in false positives, especially breath acetone, the amount of acetone exhaled by healthy individuals is relatively low and does not interfere with measurements.
However, untreated diabetic patients, fasting individuals, or those on low-carbohydrate diets may exhibit abnormally high levels of acetone in their blood and breath.
Other potential interfering substances include inhalation of toluene, gasoline, adhesives, or butane, which are industrial solvents.
Infrared spectrometers typically employ multiple (3-5) filters to eliminate interference peaks.
The conductivity method relies on the fact that gaseous alcohol adsorbed onto a heated N-type semiconductor sensor changes its conductivity characteristics; the increased conductivity can be used to estimate the alcohol concentration in the breath.
The second category of methods is based on chromatographic principles, where the breath sample is first passed through a separation column to isolate alcohol from other alcohols, aldehydes, and ketones to avoid interference, followed by detection using a thermal conductivity detector or flame ionization detector.
The third category is based on chemical principles and is further divided into "wet chemistry" and "electrochemical methods." Wet chemistry utilizes potassium dichromate (K2Cr2O7), potassium permanganate (KMnO4), or iodine pentoxide (I2O5) as oxidizing agents.
During the oxidation of alcohol to acetic acid, the color of the oxidizing agent changes (potassium dichromate changes from orange-red to green, potassium permanganate changes from purple-red to brown, and iodine pentoxide changes from colorless to blue).
The change in color is measured using a photometer, and the change is proportional to the alcohol content in the breath.
The electrochemical method involves the oxidation reaction of alcohol in a fuel cell, which releases two electrons during the formation of acetic acid, generating a current that is proportional to the alcohol content in the breath.
The breath alcohol measuring device (Breathalyzer), improved and developed by R.
F.
Brokenstein in 1954, features more functions, ease of operation, and long-term measurement stability, making it one of the most popular models at the time, still in use in many places today.
It consists of two metal cylinders; when the subject exhales into the mouthpiece, the gas is transmitted from the first metal cylinder to the second.
The second cylinder has a piston compression function that collects and discards the initial portion of the exhaled gas while retaining the later portion from deep within the lungs for testing.
Once the temperature inside the cylinder reaches 50°C, the breath sample is directed into a container containing potassium dichromate, sulfuric acid, and silver nitrate solution, forming bubbles.
The orange-red potassium dichromate solution absorbs visible light at a wavelength of 420 nm.
If alcohol is present in the breath, it will be oxidized by potassium dichromate to acetic acid, causing the potassium dichromate solution to turn green due to chromium sulfate, and the change in color measured by the photometer estimates the alcohol content in the breath.
According to current road traffic safety regulations, the standard for unsafe driving is a breath alcohol concentration of 0.25 mg/L, which converts to a blood concentration of 0.25 mg/L × 2100 = 525 mg/L.
Historical accident records indicate that driving under the influence of alcohol is a major factor in traffic accidents.
It is advisable to assume that if you have consumed alcohol, regardless of the amount, you have exceeded a breath alcohol concentration of 0.25 mg/L before being subjected to a police breath test, reminding yourself not to drive, thus protecting yourself and others; furthermore, in case of any discrepancies in breath alcohol testing, you will not be affected.
The alcohol concentration detected in the blood represents the alcohol content in the blood, and unless there is a machine malfunction or error, it will not misidentify other substances as alcohol, as this is a specific instrument.
Thank you for your inquiry, and I hope the above information addresses your concerns.
Dr.
Tsai Jue-ren, Hualien Hospital.

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Reply Date: 2007/05/05