What this test measures
Ethanol (ethyl alcohol) is the alcohol present in alcoholic drinks. After ingestion, it is absorbed rapidly from the stomach and small intestine and distributes through total body water within 30 to 90 minutes. The liver then metabolises ethanol at a near-fixed rate of about 15–20 mg/dL per hour through alcohol dehydrogenase. Serum ethanol measures the concentration circulating at the moment of sampling and correlates directly with central nervous system depression.
The assay reports a numeric value in mg/dL (Indian labs) or g/dL (some Western labs); 100 mg/dL equals 0.1 g/dL or 0.10% BAC, which is the common public-health drink-drive threshold in many jurisdictions. India's legal driving limit under the Motor Vehicles Act is 30 mg/100 mL (30 mg/dL).
Why it matters
In an emergency room a serum ethanol level helps differentiate alcohol intoxication from other causes of altered mental status — head injury, stroke, hypoglycaemia, sepsis, or poisoning with methanol, ethylene glycol, or benzodiazepines. A low or zero ethanol in an unconscious patient who smells of alcohol redirects the workup quickly. In suspected toxic alcohol ingestion the ethanol level is also used because ethanol is itself an antidote (saturates alcohol dehydrogenase before methanol/ethylene glycol can be converted to toxic metabolites).
Medico-legally, a serum (not breath) ethanol is the reference standard in India for road-traffic offences, custody cases, and post-mortem analysis. Indian hospitals also use the test to confirm acute alcohol poisoning, monitor recovery, and rule out alcohol as the cause of a presentation before discharging a patient.
How to prepare
No fasting needed. The test is most often ordered in an emergency context, so timing is dictated by the clinical event. For medico-legal sampling the skin is cleaned with a non-alcoholic antiseptic (povidone-iodine, not isopropyl wipes) to avoid contamination, and chain-of-custody documentation is maintained. If you are taking the test electively (eg. fitness-for-work assessment), abstain from alcohol for at least 24 hours beforehand.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Ethanol (mg/dL)[1][2][3] | Not detected (< 10 mg/dL) | Ethanol is not normally present in serum. A "not detected" result rules out recent alcohol consumption (within the past few hours). | 20–50 mg/dL: mild impairment, reduced judgement. 80–100 mg/dL: clear intoxication; above India's 30 mg/dL legal limit. 100–200 mg/dL: pronounced ataxia, slurred speech. 200–300 mg/dL: severe intoxication, possible vomiting and stupor. > 300 mg/dL: risk of coma, respiratory depression, and death — especially in non-tolerant drinkers. |
Serum ethanol levels and clinical effects
| Serum ethanol (mg/dL) | BAC equivalent | Typical effect |
|---|---|---|
| < 10 | < 0.01% | Not detected; no recent intake |
| 20 – 50 | 0.02 – 0.05% | Mild euphoria, reduced inhibition |
| 50 – 100 | 0.05 – 0.10% | Impaired judgement and coordination; above India's 30 mg/dL legal driving limit |
| 100 – 200 | 0.10 – 0.20% | Slurred speech, ataxia, clear intoxication |
| 200 – 300 | 0.20 – 0.30% | Confusion, vomiting, possible stupor |
| 300 – 400 | 0.30 – 0.40% | Coma risk, severe respiratory depression |
| > 400 | > 0.40% | High risk of death without supportive care |
Frequently asked questions
Is a blood alcohol test the same as a breathalyser?
No. A breathalyser estimates blood alcohol from breath using a fixed ratio. A serum ethanol test directly measures alcohol in a venous blood sample and is more accurate and legally robust — used in hospitals and for medico-legal cases.
What is the legal alcohol limit for driving in India?
Under the Motor Vehicles Act 1988, the legal limit is 30 mg of alcohol per 100 mL of blood (30 mg/dL). Many other countries allow up to 80 mg/dL, but India is stricter. For commercial drivers and learners many states enforce a zero-tolerance policy.
How long does alcohol stay in the blood?
The liver clears ethanol at roughly 15–20 mg/dL per hour. Someone with a level of 150 mg/dL takes about 8–10 hours to become legally sober. Hydration, food, and "coffee" do not speed this up — only time does.
Why is the skin cleaned without alcohol before the test?
Standard isopropyl-alcohol skin wipes can contaminate the sample and falsely elevate the result. Hospitals and medico-legal labs use povidone-iodine or chlorhexidine without alcohol, and document this in the chain-of-custody form.
Can medicines or mouthwash give a false positive?
Some cough syrups, mouthwashes, and asthma inhalers contain small amounts of ethanol but rarely produce a serum level above 10 mg/dL. Diabetic ketoacidosis can produce acetone that interferes with older breathalyser machines but not with modern serum assays.
Is alcohol detectable in blood after 24 hours?
For most social drinkers, ethanol falls below the detection limit within 12–24 hours of the last drink. Metabolites (ethyl glucuronide, ethyl sulphate) remain detectable in urine for 24–72 hours and are sometimes used in abstinence monitoring — but the standard serum ethanol test does not detect them.
When is this test ordered?
Common indications include altered mental status in the emergency room, suspected acute alcohol poisoning, evaluation of unexplained acidosis (rule out methanol or ethylene glycol), road-traffic medico-legal cases, custody and fitness-for-work assessments, and pre-employment screening in some industries.
Related Drugs / Therapeutic Monitoring tests
Tests commonly ordered alongside ETHANOL, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Blood Alcohol Level · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Ethanol Toxicity · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Ethanol, Serum · accessed 2026-05-30T00:00:00.000Z
- CDC — Alcohol and Public Health · accessed 2026-05-30T00:00:00.000Z
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