Alcohol
Norm
Less than 0.1 per mille (g/l)
or g/l
mg/dl less than 10 mg/dl
SI system less than 2mmol/l
Synonyms: ethyl alcohol, ethanol, EtOH.
Blood, serum
If a sample is to be stored for a long time, a gray cap (sodium fluoride) is used.
When taking blood for testing, the skin should not be disinfected with alcohol (ethanol, iodine alcohol solution, etc.). In forensic medicine, ethanol concentration in the blood is more commonly measured in per mille. If the result is presented in g/l, its numerical expression is equivalent to per mille. A life-threatening concentration of ethanol in the blood is considered to be above 4.5g/l (4.5 per mille). A coma state occurs when the alcohol concentration in the blood is between 3.5–4.5g/l (3.5–4.5 per mille). If a random test shows 3 per mille (3.0g/l) or if a patient is found with 1 per mille (1.0g/l) of ethanol concentration upon admission to a healthcare facility, there is a high likelihood of alcohol abuse by the patient. A more specific test to determine chronic alcoholism is the determination of carbohydrate-deficient transferrin (see carbohydrate-deficient transferrin). Hematological analyzer MCV and biochemical indicator GGT (gamma-glutamyltransferase) also allow suspicion of chronic alcoholism. Other laboratory parameters often change with alcohol consumption. The following may occur:
- hypoglycemia;
- hypochloremic alkalosis;
- hypomagnesemia;
- increased lactate concentration;
- metabolic acidosis with an increased anion gap;
- ketoaciduria;
- thrombocytopenia;
- megaloblastic and hemolytic anemias;
- increased uric acid concentration;
- increased liver enzyme activity: AST, ALT, alkaline phosphatase;
- increased bilirubin concentration;
- increased triglyceride concentration. In individuals with chronic alcoholism, the concentration of folic acid decreases. This is because folic acid reserves accumulate in the liver.
Alcohol determination is performed to determine the cause of intoxication or coma. This test is important when examining unconscious patients. In cases of intoxication, a negative alcohol test may suggest other causes: ketoacidosis or ethylene glycol poisoning. A positive alcohol test in the blood may indicate not only ethanol but also isopropanol intoxication.
Ethyl alcohol is absorbed in the oral mucosa, stomach, and small intestine. The maximum alcohol concentration in the blood is reached within 40–70 minutes when alcohol is consumed on an empty stomach. Food in the stomach significantly slows down alcohol absorption (especially fatty foods). After absorption, alcohol quickly spreads in tissues (absorption period). About 2 hours after alcohol consumption, a diffuse equilibrium is established between the alcohol in the blood and tissues. When this state is reached in the blood, a gradual decrease in alcohol concentration in the blood begins (elimination period). Alcohol concentration decreases in the blood due to its oxidation in the liver by the enzyme alcohol dehydrogenase (80% of absorbed alcohol is metabolized this way). About 10% of absorbed alcohol is excreted through urine, sweat, and exhalation. The increase and decrease of ethanol concentration in the blood occur at a constant rate (absorption and elimination phases have a linear relationship). During the elimination period, alcohol concentration in the blood decreases on average by 0.15–0.2 per mille (3.2–4.62mmol/l) per hour (depending on individual weight, liver function, and other factors). For lean, exhausted individuals, alcohol concentration in the blood decreases at a faster rate (approximately 0.3 per mille per hour). In obese individuals, the rate of alcohol elimination is slower. In individuals with alcohol dependence who frequently consume alcohol, elimination may be several times faster. For these individuals, the elimination period of alcohol may not have a linear relationship. The rate of alcohol elimination can be influenced by food, environmental temperature, physical activity (e.g., elimination is faster during intense work or exercise, slower during sleep). Alcohol is metabolized in the liver – liver diseases can affect the duration and nature of intoxication. The female body absorbs alcohol faster than the male body. After consuming the same dose of alcohol, women have a 35–45% higher concentration in the blood than men. The elimination rate in women’s bodies is also slightly higher. A higher concentration in women’s blood is found during the premenstrual period and when taking contraceptive pills. According to J. Wallach, 30g of whiskey, a glass of wine, and about 400g of beer increase blood alcohol concentration by 0.15–0.25g/l (0.15–0.25 per mille). Alcohol concentration in the blood also increases faster in elderly individuals. The average ratio of alcohol in urine/blood is 1:1.35. The average ratio in saliva/blood is 1:20. Serum alcohol levels are 10–15% higher than blood alcohol concentration from the same blood sample. For example, 1.12 per mille in serum is approximately equivalent to 1.00 per mille in blood. Knowing how alcohol concentration decreased can help assess what it was at a certain moment in time (e.g., during a car accident). By determining alcohol concentration in the blood, conclusions can be drawn about its concentration throughout the body and the degree of intoxication.
In urine, the concentration of alcohol lags behind the blood concentration during the absorption period. Approximately after 2.5-3 hours, an inverse relationship between blood and urine concentration is established: the amount of alcohol in urine is higher than in blood (the ratio in urine and blood is approximately 1.2-1). As the elimination process progresses, a state is established where alcohol is no longer found in the blood, but it can still be detected in urine. However, the concentration of alcohol in urine poorly correlates with the blood alcohol concentration. Therefore, the urine alcohol indicator cannot be used to assess the degree of intoxication. With an increased alcohol concentration in the blood, an increased osmotic gap is detected. The increased osmotic gap (the difference between the osmolality determined by calculation and the osmolality determined by an analyzer) usually exceeds 10 mmol/kg. If no increase in osmotic gap is found, then the possibility of increased concentrations of ethanol, methanol, and ethylene glycol in the blood can be ruled out. In the case of coma, the alcohol concentration in the blood must be no less than 3.0g/l (3 promiles). If this concentration is lower, then there may be another cause. It is not uncommon for cases where alcohol and other narcotic substances are abused together.
Source | Handbook of Basic Laboratory Tests | Doctor of Medical Sciences Gintaras Zaleskis