Alcohol (Ethanol, Ethyl Alcohol)

Blood Alcohol 

Ethyl alcohol (ethanol) 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. 

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 by men and 35 to 40 g by women is believed to increase the risk of liver disease.  

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 30 mg/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:

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

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 80 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.  

Most hospital laboratories measure ethanol using a rapid enzymatic method on an automated chemistry analyzer. The principle of the ethanol test is that ADH catalyses the oxidation of ethanol to acetaldehyde with the concurrent reduction of NAD+ to NADH. The system monitors the rate of change in absorbance due to NADH at 340 nm.

Isopropyl alcohol may interfere with the measurement of ethanol by 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 0-5 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.  

Alcohol, Urine

When alcohol is ingested, it is absorbed directly from the proximal small intestine and distributed throughout the entire fluid space of the body.  After equilibrium is reached,  alcohol will be found in all tissues of the body in proportion to their water content.  Urine is the most practical specimen for alcohol testing in the workplace, when the purpose of testing is to demonstrate that alcohol consumption has occurred.  Peak urine alcohol levels are reached 45 to 60 minutes after alcohol ingestion.  At this time, urine alcohol levels are typically about 1.3 times greater than the corresponding blood alcohol concentration.  This ratio is only valid during the elimination phase, which occurs after the blood alcohol level has peaked and is decreasing.  Alcohol may be detected in the urine for 1 to 2 hours longer than it is detected in blood. 

The presence of alcohol in the urine indicates recent prior use, but may not correlate with the degree of intoxication observed at the time the specimen is provided. Increments of urine continuously pool in the bladder, and each contains a different amount of ethanol.  The ethanol level from such a sample relates only to the average blood alcohol concentration during the time needed for the voided urine sample to accumulate in the bladder and not to the blood alcohol concentration at the time of collection. 

False negative results may be caused by the volatility of alcohol. Urine alcohol concentrations may decrease 10 to 25% during each hour that a urine sample remains uncapped prior to testing.  

Diabetic patients who are spilling glucose into their urine and have a urinary tract infection with a fermenting organism, like Candida albicans, may have a positive test even though they did not consume alcohol.  

Estimation of blood alcohol concentration from urine alcohol measurements is more reliable if two urine samples are collected about 30 minutes apart. The first urine is usually discarded and the second one is used to estimate blood alcohol concentration. The limitation of a single first-void urine sample is that one does not know over what time period the urine has collected in the bladder. However, subjects who have been drinking usually do not retain urine in their bladders for an extended time period because of the diuretic effect of alcohol.  

At least 35 states authorize urine alcohol measurements for driving related offenses.  Some regulatory and legal agencies use a 1.5:1 urine to blood ratio, instead of 1.3:1, to be conservative and give the benefit of any doubt to the subject.  

Reference value is not detected. 

Specimen requirement is a freshly voided random urine sample of 25 mL. A Drug Screen Kit should be used for chain of custody testing.

References

Penetar DM, McNeil JF, Ryan ET, Lukas SE. Comparison among plasma, serum, and whole blood ethanol concentrations: impact of storage conditions and collection tubes. J Anal Toxicol. 2008 Sep;32(7):505-10.