Understanding Alcohol and Blood: The Basics
Alcohol is one of the oldest substances known to mankind, but it effects are continually being studied, re-studied, and analyzed. Beverage alcohol is commonly referred to as "ethanol" or "ethyl alcohol" as well as "alcohol." Ethanol is one of a family of alcohols which includes methanol (methyl alcohol or "wood alcohol"), 1-Propanol (propyl alcohol), 1-Butanol (butyl alcohol), 2-Propanol (isopropyl alcohol or "rubbing alcohol"), and ethanediol (ethylene glycol or "antifreeze").
Common Alcohol Compounds
Common Name     IUPAC     Formula
Methyl alcohol    Methanol    CH3OH
Ethyl alcohol     Ethanol    CH3CH2OH
n-Propyl alcohol    1-Propanol    CH3CH2CH2OH
Isopropyl alcohol    2-Propanol    (CH3)2CHOH
n-Butyl alcohol     1-Butanol      CH3 (CH2)2CH2OH
Ethyl alcohol (ethanol) is a very small molecule that is completely soluble (miscible) in water. Ethanol is lighter than water (specific gravity = 0.789) and has a boiling point at 78 degrees Celsius. The fact that alcohol is both lighter than water and boils at a lower boiling point is essential in the distillation process. The main source of consumed alcohol is commercially prepared beverages: fermented alcoholic beverages and distilled alcoholic beverages. Beer and wine are typical fermented beverages. In both cases, a natural product (barley in the case of beer and grapes in the case of wine) is fermented by the addition of yeast microorganisms. The alcohol that is produced is the waste byproduct of the metabolism of the yeast's or bacteria's consumption of sugars found in the natural product. Throughout the remainder of this discussion, the terms ethanol and alcohol may be used interchangeably.
Ethanol in Beverages Fermented Beverages: Wine ethanol concentrations generally range from 10-12% from the fermentation of crushed grapes, but may be "fortified" by the introduction of additional alcohol during the production process. Most table wine sold in the state of Alabama is 12.5% ethanol by volume . Most commonly, beer with a 3.2-5% ethanol concentration is sold within the state. Beer ethanol concentrations when fermented can range from 3% to as high as 15%, but are regulated by state law to not exceed 6% alcohol by volume .
Distilled Beverages: Production of distilled alcoholic beverages begins with the fermentation of one or more natural grains such as corn, wheat, rye, barley. These grains are the source of carbohydrates (sugars) necessary for the process. The result is a wort (fermented fluid) containing up to 12% ethanol by volume, which is then distilled by heating. Alcohol (ethanol), which evaporates at 78 degrees Celsius, travels into a cooling apparatus (condenser) where it re-liquefies. The now-concentrated ethanol can be collected in a storage container, and given flavorings. Whiskey, vodka, gin, and a variety of other alcohol beverages are produced in this manner. What distinguishes the various beverage types is the carbohydrate source (grain).
Homemade distilled ethanol, commonly referred to as "moonshine", while generally having no flavoring added, possesses a fruit-like odor. The ethanol concentration in "moonshine" can range from the low 60-proof range (30% ethanol) to as high as 120-proof (60% ethanol). The name "moonshine" is derived from the nocturnal, clandestine nature of this illicit beverage production .
Ethanol is classified as a 'Central Nervous System' depressant (CNS) whose impairing effects are in proportion to its presence in the CNS. However, blood rather than brain tissue is the preferred representative specimen for a chemical test for impairment because blood delivers ethanol to the CNS and thereby accurately reflects CNS exposure to ethanol. A large body of research exists which relates ethanol concentrations in whole blood with human performance. Whereas any biological specimen may be analyzed for ethanol (blood, plasma, serum, urine, ocular fluid, tissues), results for whole blood provide an accepted, uniform standard for interpretations. For these reasons, statutes typically base per se limits for ethanol content in whole blood (or breath, which is a related, but different subject, and is not addressed in this publication). Forensic ethanol analyses are conducted with whole blood when it is available. Determining a subject's blood alcohol concentration (BAC) is the single most important issue in establishing criminal and civil liability in a judicial proceeding where alcohol is alleged to have been an element of the offense or the cause of action.
Absorption Principles: Whereas the entire gastro-intestinal tract (GI) is capable of alcohol absorption, almost 90% takes place in the small intestine where structural microvilli greatly increase the surface area of the gut available for absorption. With its small molecular size, ethanol readily crosses the GI tract membranes via passive diffusion and enters the circulation, mixing completely with the fluid portion of blood (blood is approximately 85% water). Ethanol then distributes throughout the body where it rapidly crosses back through membranes into the tissues and, most significantly, across the blood-brain barrier. Blood: The adult human contains approximately five liters of blood, constituting about 8% of the total body weight. Whole blood is a complex, heterogeneous mixture of solid material and fluid. The solid material comprises red blood cells (erythrocytes), platelets (thrombocytes), and white blood cells (leucocytes - lymphocytes and phagocytes). Each cell type has a specific function: o Red blood cells contain hemoglobin which binds oxygen and transports it throughout the body. o Platelets participate in forming blood clots o White blood cells are responsible for cell-mediated immune responses to foreign organisms
There are approximately 500 times more erythrocytes than leukocytes. The volume portion of whole blood occupied by red cells is the hematocrit (HCT), which is defined as the volume of red cells divided by the total blood volume. An average HCT for adult males is 40% to 50% and for adult females, 35% to 45%. The HCT changes with age. A low HCT indicates a relatively lower content of red blood cells in whole blood, which may be due to anemia, blood loss (internal or external) or other disease conditions.
The fluid portion of whole blood is called plasma, which may be prepared by removing the cellular solids from unclotted blood (typically by centrifugation). Serum is the fluid portion of whole blood remaining after the blood has clotted and the clot is removed. Because plasma and serum contain no cellular solids, they contain a relatively greater content of water than does whole blood. This is significant because ethanol distributes into the various body compartments in proportion to their water content. In that regard, plasma and serum, with a water content of 95% to 97% will contain more ethanol than the whole blood from which they are derived (approximately 85% water). This difference, 10% to 15%, highlights the importance of establishing what specimen - whole blood or plasma - was tested for ethanol before making any interpretations of the results.
Blood alcohol concentration: Results of forensic analyses are typically expressed as a grams of ethanol per 100 mL of specimen or grams percent (g %) or simply percent (%). That a blood ethanol concentration was reported to be 0.080 g/100 mL, however, does not imply that 100 mL of blood was analyzed and 0.080 grams of ethanol were detected. The standard paractice in reference laboratories is to analyze 100 microliters (0.10 mL or 100 millionths of a liter) of specimen.