Alcohol is the term given to name a family of organic compounds that all have common properties. Ethanol, methanol, isopropanol, and other compounds are all members of the alcohol family. Ethanol is the alcohol that is seen most often ingested by patients. The chemical formula for ethanol is C2H5OH and is usually abbreviated ETOH. The main characteristic of ethanol is that it is very soluble in water, which allows it to be taken up quickly by the human body. There are two types of ethanol, that which is made for human consumption and that which is made for industrial purposes. The difference between the two is the way in which they are processed. Ethanol for human consumption is made from fermenting foodstuffs such as barley or grapes. Ethanol for industrial purposes is made using chemical processes that render the final product unsafe for consumption. In the laboratory testing is done for ethanol that is made for human consumption.
Ethanol is the member of the alcohol family that is normally consumed by people. When it enters the body it is absorbed into the bloodstream by the stomach and the small intestine. Ethanol is readily absorbed into the bloodstream due to its high affinity for water. Once in the bloodstream it is carried throughout the body and will affect all tissues that contain water. Once all the ethanol in a person’s system has been absorbed equilibrium will be reached throughout the body so that all tissues in a person’s system will have the same concentration of ethanol. When a person consumes ethanol the stomach absorbs approximately 20% of the ethanol and the small intestine absorbs approximately 80%. The longer ethanol remains in the stomach, say when you eat a big meal and drink, the slower the rate of absorption. If a person drinks ethanol on an empty stomach the ethanol is quickly absorbed into the blood stream via the small intestine. The rate of absorption affects the rate that ethanol takes to affect the system. Ethanol is considered a central nervous system depressant. It affects the body by reducing inhibitions, reducing response to stimuli, and impairs a person’s thought process. Ethanol is toxic to the body and is metabolized via the liver. Ninety-five percent of ethanol in the body is metabolized by the liver. The remaining ethanol is excreted through the lungs and in the urine. The liver metabolizes alcohol through a variety of pathways, however the main enzyme that breaks ethanol down is alcohol dehydrogenase. This enzyme breaks ethanol down into acetaldehyde, which is then broken down into acetic acid. Finally the acetic acid is broken down into carbon dioxide and water. Ethanol acts as a diuretic which causes the body to lose water through urination. Since the liver needs water in order to metabolize ethanol it will divert water from all areas of the body if there is a not sufficient amount of water present. This lack of water available to the liver and the toxicity of the metabolite acetaldehyde both contribute to the systemic affects of ethanol on the body. These affects include the common hangover complaints such as nausea, vomiting, and headaches. The rule of thumb is that a healthy individual will eliminate approximately 15 mL of ethanol (one beer or glass of wine) per hour. Chronic alcoholics generally will metabolize ethanol at a higher rate so long as the liver is still relatively healthy. With age, our ability to process alcohol diminishes.
In the laboratory there are several ways to test for ethanol. Ethanol can be found in the blood, in the urine, and in a person’s breath. These are good samples for ethanol testing. Generally laboratories will process blood and urine to determine ethanol concentrations while field workers, such as the police, will use a breathalyzer to determine ethanol concentration in a person’s breath. The results produced by the lab are used by doctors to determine ethanol intoxication and poisoning. The method used on the Siemens Dimension system is based on an enzymatic reaction. The reagent used contains alcohol dehydrogenase and the co-enzyme NAD (nicotinamide adenine dinucleotide). If ethanol is present in a serum sample it reacts with the NAD in the presence of the enzyme alcohol dehydrogenase to produce acetaldehyde and NADH. The amount of NADH produced is read via absorbance at 340nm and is proportional to the amount of ethanol in the sample. In general the normal range for ethanol is zero however some laboratories will report out less than ten to rule out samples that have been contaminated with alcohol wipes. Positive results are reported out in mg/dL for the Siemens Dimenson system. The national blood alcohol concentration (BAC) values that define legal limits for alcohol intoxication are reported out in a percentage. The legal limit of 0.08% means that there are eight grams of alcohol per every hundred mL of blood in a person’s system. To compare this value to the values reported out on the Siemens Dimension system a 0.08% BAC level would be equivalent to a value of 80 mg/dL. It is generally accepted that values over 0.40 BAC or 400 mg/dL can be fatal in a normal healthy person.
Ethanol is the most commonly abused substance in the country. Here in Virginia the legal limit for alcohol intoxication is 0.08% BAC. In some instances an ethanol level can be used for legal purposes, however in these cases samples have to be collected and tested following chain of custody protocols. The role of the laboratory is to test samples for the presence of ethanol so that doctors can treat patients for intoxication or poisoning.
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· SIEMENS Dimension Flex reagent cartridge. (2009). Ethanol. (REF DF22). Newark, DE: Siemens Healthcare Diagnostics Inc.
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