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Alcohol (Ethanol, Ethyl Alcohol)

Ethyl alcohol is a central nervous system depressant and an anesthetic. Alcohol ingestion may cause loss of judgment, incoordination, and disorientation. Higher doses may induce stupor possibly followed by coma and death.

Blood Alcohol Concentration

Clinical Signs & Symptoms

10 – 50 mg/dL

0.01 – 0.05 g/dL

Mild euphoria, decreased inhibitions, diminished attention & judgement

50 – 100 mg/dL

0.05 – 0.10 g/dL

Euphoria, sedation, impaired coordination, decreased sensory responses to stimuli, decreased judgement

150 – 300 mg/dL

0.15 – 0.30 g/dL

Confusion, disorientation, impaired balance, slurred speech

250 – 400 mg/dL

0.25 – 0.40 g/dL

Sleep or stupor, marked muscular incoordination, markedly decreased response to stimuli, incontinence

400 – 500 mg/dL

0.40 – 0.50 g/dL

Coma, hypothermia, respiratory & circulatory failure, possible death

Ethyl alcohol is absorbed rapidly in the proximal small intestine, usually within 30 to 90 minutes after ingestion. More than 90% of ethanol is metabolized by hepatic microsomal mixed function oxidases to acetaldehyde and acetic acid. The primary enzyme, alcohol dehydrogenase, is concentrated in the liver, but smaller concentrations are found in the gastric mucosa. Women may have less gastric alcohol dehydrogenase activity than men, explaining their increased bioavailability and higher peak ethanol levels. Aspirin and histamine-2 blockers may inhibit gastric alcohol dehydrogenase activity, causing slightly elevated blood ethanol levels. Other drugs that are metabolized by the hepatic microsomal system such as phenobarbital increase the effect of ethyl alcohol. Daily consumption of 70 to 80 g of alcohol is believed to increase the risk of liver disease for men and 35 to 40 g daily increases the risk for women.

Blood alcohol levels vary depending on the amount consumed, the time elapsed since consumption, metabolic rate, and body weight. Ethanol clearance is nonlinear at concentrations above 20 mg/dL and changes with alcohol concentration. Generally, ethanol metabolism occurs at a rate of 10 to 30mg/dL per hour. The average elimination rate is12+/- 4 mg/dL per hour for nondrinkers, 15+/-4 mg/dL per hour for social drinkers, and 30+/-9 mg/dL per hour for alcoholic persons. Children have a higher average metabolic rate of approximately 28 mg/dL per hour.

A standard drink contains approximately 13 g of absolute alcohol and is often defined as one ounce of 100 proof hard liquor, 1.5 ounces of 80 proof liquor, one 12-ounce beer, or 5 ounces of wine. The ethanol content of a beverage can be calculated using the following formula: D(g) = F x Volume (mL) x 0.8 g/mL where

  • D = grams of ethanol in the drink
  • F = fraction of ethanol (%v/v)
  • Volume = volume of beverage in mL (1 ounce = 30 mL)
  • 0.8 g/mL = specific gravity of ethanol

For example, the total amount of ethanol in 1.5 ounces of 80 proof whiskey would be calculated as follows: 0.40%v/v x (1.5 oz x 30 mL/oz) x 0.8 g/mL = 14 g.

Household products have the following ethanol content:



After shave


Rubbing alcohol


Paint stripper




Dish wash detergent


Denatured alcohol


Glass cleaner


Cough medicine/elixir


Hair tonic


Solid can fuel




The expected blood alcohol level obtained within one hour of consumption can be estimated from the following table.

Number of drinks consumed by a 55 kg person

Number of drinks consumed by a 90 kg person

Approximate blood alcohol concentration (mg/dL)



50 – 100



100 - 150



150 – 200



200 – 300



300 – 400




Substantial impairment can occur at alcohol levels <100 mg/dL. Deterioration of driving skills can occur at levels <50 mg/dL and maneuvers to avoid a crash, such as steering and applying brakes can be compromised at concentrations of about 30 mg/dL. Legal intoxication limits are inconsistent throughout the United States. The majority of states have set legal limits at 100 mg/dL, while others have lowered the limit to 80 mg/dL. The Kansas and Missouri legal intoxication level is 100 mg/dL.

A legal blood alcohol concentration is often expressed as the percentage of alcohol by weight (i.e. grams of ethanol in 100 mL of blood). Clinical laboratories generally report ethanol concentration in mg per dL of blood. Lab values can be converted to blood alcohol concentration by moving the decimal point three places to the left. For example, 135 mg/dL becomes 0.135% wt/vol. This value is then truncated to two digits, becoming 0.13% wt/vol or 0.13 g/dL.

The water content of serum and whole blood is 98% and 86%, respectively. Because ethanol preferentially partitions into the aqueous rather than the cellular phase of blood, higher levels are obtained with serum or plasma. Serum and plasma levels average 1.09 to 1.18 times higher than whole blood levels. The concentration of ethanol in arterial and capillary blood is about 25% higher than venous blood after initial consumption of alcohol.

Isopropyl alcohol may interfere with this method, giving falsely elevated values. Isopropyl alcohol has a stronger intoxicating effect than ethyl alcohol and should be suspected when a patient appears very intoxicated and his blood alcohol is low (below 100 mg/dL). Methanol and acetone do not cause significant interference. This test is satisfactory for medical, but not legal use.

Reference range is 0 - 9 mg/dL .

Specimen requirement is one SST tube of blood. Venipuncture site should be cleansed with benzalkonium chloride or aqueous povidone-iodine and NOT alcohol. The use of an alcohol swab may falsely elevate the blood level. Serum should be immediately separated from the red blood cells and analyzed within 4 hours when collected without preservatives. Specimens should be kept sealed, because ethanol is volatile. Serum or plasma can be stored frozen.

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