Equivalent Limits in Other Body Fluids

Statutes have been used to establish blood alcohol concentration equivalents in other tissues and breath. Not infrequently, alcohol concentrations will be measured in accident victims taken for treatment at trauma centers. However, there are two important differences between alcohol measurements made in hospitals and those made in forensic laboratories; first, in hospitals, standard international units are the norm, the mole is the unit of mass, the liter is the unit of volume, and alcohol concentrations are reported in mmol/L. In forensic laboratories, results are expressed as gram/deciliter or liter, or even milligrams per milliliter, and measurements are made in whole blood, not serum or plasma. Because 1 mL of whole blood weighs, on average, 1.055 g, a blood alcohol concentration of 100 mg/dL is actually the same as 95 mg/ 100 g or 21.7 mmol/L (17).

There is another, even more important, difference between serum/plasma and whole blood. The former contains 91.8% water, whereas the latter contains only 80.1% water. Because alcohol has a large volume of distribution, this difference in water content means that alcohol concentrations measured in serum/plasma will be higher than concentrations measured in whole blood by approx 14%. In practice, if plasma alcohol concentrations are to be introduced as evidence, they should be related back to whole blood concentrations using an even higher ratio (1.22:1), which corresponds to the mean value, ± 2 standard deviations. As mentioned, if whole blood is tested, drivers are not usually prosecuted at blood levels below 87 mg/100 mL of blood (17).

Breath testing is equally problematic. The instruments used are calibrated to estimate the concentrations of alcohol in whole blood, not plasma or serum. To estimate the serum or plasma alcohol concentration from breath measurements, a plasma/breath ratio of 2600:1 must be used (because, as explained, whole blood contains 14% less alcohol). In Europe, but not necessarily in the United States, two specimens of breath are taken for analysis, and the specimen with the lower proportion of alcohol should be used as evidence.

Bladder urine, because it contains alcohol (or other drugs) that may have accumulated over a long period, is generally not considered a suitable specimen for forensic testing, especially because the presence of alcohol in the

Table 1

Prescribed Blood Alcohol Levels in Various Jurisdictions

Table 1

Prescribed Blood Alcohol Levels in Various Jurisdictions

Australia

50

France

50

Poland

20

Austria

80

Germany

80

Romania

0

Belgium

80

Greece

50

Russia

0

Bulgaria

0

Hungary

0

Sweden

20

Canada

80

Italy

80

Spain

80

Czechoslovakia

80

Luxembourg

80

Turkey

0

Denmark

80

Netherlands

50

United States

100a

Ireland

80

Norway

50

Yugoslavia

50

Finland

50

a Some states in the United States have reduced the legal level to 80 mg/100 mL of blood.

a Some states in the United States have reduced the legal level to 80 mg/100 mL of blood.

urine only proves that alcohol is present in the body. Alcohol concentrations in bladder urine cannot be used to infer the blood levels reliably. Even so, UK legislation and most US states still allow drivers the option of providing breath, blood, or urine specimens, but, as of 1999, the State of California has dropped the option of providing urine samples, and other states are considering similar actions. Under the new California provisions, police can still request a urine test if a suspect's breath test is negative (22).

Other options are available in the case of alcohol-related fatalities. Comparison of alcohol concentrations in vitreous and blood can provide a good indication of whether concentrations were rising or falling at the time of death (alcohol is distributed mainly in water and the water content of vitreous is lower than that of blood). Urine obtained from the kidney pelvis can also be used, because its alcohol content can be precisely related to blood concentration (23).

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