Blood Sciences Test



Serum or Plasma (EDTA or Lithium Heparin)


mg/100 ml (mg/dL)

Reference Range

To convert mmol/L to mg/100 ml (mg%), multiply by 4.6

Test Usage

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

<80 mg/100 ml

(17.4 mmol/L)

UK legal drink-driving limit

50-100 mg/100 ml

(10.8 – 21.7 mmol/L)

Decreased reaction time, diminished judgement, fine motor incoordination

100-200 mg/100 ml

(21.7 – 43.4 mmol/L)

Blurred vision, aggression, disorientation, confusion, ataxia, vasodilation, stupor, vomiting, sweating

200-450 mg/100 ml

(43.4 – 98 mmol/L)

Marked incoordination, coma, hypothermia, hypoglycaemia and potential convulsions

>450 mg/100 ml

(>98 mmol/L)

Respiratory depression, hypotension, loss of protective airway reflexes (risk of aspiration), hypothermia, incontinence, coma, hypoglycaemia and convulsions. Potentially fatal.

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 30 mg/dL per hour. The average elimination rate is 12+/- 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:

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. 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.

Patient Preparation

Do not use alcohol or other volatile disinfectants at the site of venepuncture. Aqueous Zephiran (benzalkonium chloride), aqueous Merthiolate (thimerosal), or povidone-iodine may be used.


Local test

Turnaround Time

1 day Cannot be added on to an existing request >4 hours old.

Specimen Labelling Procedure