Toxicology
Ethanol (alcohol)
Ethanol is the alcohol found in beverages and in many sanitisers and solvents, and it is measured to gauge recent alcohol intake and the degree of intoxication. At or near the patient it can be screened in breath or saliva within a couple of minutes, while serum, plasma or whole blood is used for quantitative laboratory confirmation.
Why it is measured
Rapid ethanol testing helps clinicians judge whether reduced consciousness or altered behaviour is driven by alcohol or by another cause, and it underpins occupational, forensic and driving-impairment screening.
| Typical range | There is no physiological reference range because ethanol is exogenous. When a person has not been drinking, the expected result is none detected, typically below 10 mg/100mL (about 2 mmol/L). For context, the UK legal driving limit is 80 mg/100mL of blood (0.08% BAC, roughly 17 mmol/L) in England, Wales and Northern Ireland, and 50 mg/100mL (about 11 mmol/L) in Scotland. The corresponding breath limits are 35 micrograms per 100mL of breath in England, Wales and Northern Ireland and 22 micrograms per 100mL in Scotland. The Q.E.D. A150 saliva test quantifies ethanol across 0 to 150 mg/dL. Cut-offs and units vary by method, sample matrix (blood, serum, breath or saliva) and jurisdiction, so always state the matrix; 1 mmol/L is about 4.61 mg/dL. |
|---|---|
| Sample | Oral fluid (saliva) or exhaled breath for point-of-care screening; serum, plasma or whole blood for quantitative laboratory measurement. Urine is sometimes used as an additional screening matrix. Avoid alcohol-based skin antiseptic at the puncture site for blood sampling. |
| Turnaround | About 1 to 3 minutes for breath and saliva point-of-care devices; a few minutes for a laboratory enzymatic assay once the sample has been processed. |
Point of care devices that report it
- OraSure Q.E.D. A150 Saliva Alcohol Test (quantitative saliva ethanol, CLIA-waived)
- Dräger Alcotest breath alcohol analysers (e.g. Alcotest 5000, 7000, 9510)
- Intoximeters Alco-Sensor breath alcohol analysers
- Lifeloc breath alcohol testers
- AlcoScreen saliva alcohol screening strips
Questions, answered
Does a saliva or breath point-of-care result equal a blood alcohol concentration?
These tests estimate the blood alcohol concentration and correlate well with it, but they are screening tools. Where a definitive or legally defensible figure is needed, a confirmatory blood or serum measurement by an accredited laboratory is used.
Why can a serum ethanol value look higher than a whole-blood value for the same person?
Serum and plasma contain more water than whole blood, so enzymatic serum assays typically read roughly 10 to 18 percent higher than whole-blood results. The matrix and method should always be recorded when results are compared.
Can mouthwash or hand sanitiser affect the reading?
Residual alcohol in the mouth from mouthwash, a recent drink or some sprays can transiently raise breath and saliva readings, which is why an observation period before testing is advised. Alcohol-based skin antiseptic at a blood puncture site can likewise be a source of contamination.