EtG vs BAC: What's the Difference?
Both measure alcohol, but they work in completely different ways. Understanding these differences is crucial for knowing what to expect from each test.
Editorial note
This educational page is maintained by EtGCalc and reviewed against published EtG research, SAMHSA guidance, and our calculator methodology. It does not provide medical or legal advice.
BAC Testing
Measures current intoxication level by detecting alcohol in blood or breath.
EtG Testing
Measures a metabolite of alcohol to detect past consumption, even after sobriety.
Side-by-Side Comparison
| Feature | BAC | EtG |
|---|---|---|
| What it measures | Alcohol in bloodstream | Ethyl Glucuronide (metabolite) |
| Detection window | 6-12 hours max | 24-80 hours |
| Sample type | Blood, breath, or saliva | Urine (primary), hair |
| What it proves | Current impairment | Past alcohol consumption |
| Common uses | DUI stops, workplace random | Probation, custody, treatment |
| Legal limit | 0.08% (driving) | 100-500 ng/mL (varies) |
| False positive risk | Very low | Low (at 500 cutoff) |
Understanding BAC (Blood Alcohol Concentration)
How BAC Works
BAC measures the percentage of alcohol in your bloodstream. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. This directly correlates with impairment level.
BAC Elimination Rate
The liver processes alcohol at a relatively constant rate:
~0.015% per hour
(approximately one standard drink per hour)
BAC Testing Methods
Most common, instant results
Most accurate, lab required
Non-invasive, moderately accurate
Understanding EtG (Ethyl Glucuronide)
How EtG Works
When your liver processes alcohol, about 0.02-0.06% is converted to Ethyl Glucuronide (EtG). This metabolite stays in your system long after the alcohol itself is gone, making it useful for detecting past drinking.
EtG Timeline
EtG Cutoff Levels
When Each Test Is Used
BAC is used for:
- Traffic stops and DUI enforcement
- Post-accident workplace testing
- Determining current impairment level
- Emergency room assessments
EtG is used for:
- Probation and parole monitoring
- Child custody agreements
- Alcohol treatment programs
- Professional licensing (healthcare, aviation)
Key Takeaways
- 1
BAC measures current intoxication — it tells you if someone is drunk right now.
- 2
EtG measures past consumption — it tells you if someone drank in the last few days.
- 3
You can pass a BAC test and fail an EtG test — being sober doesn't mean EtG is gone.
- 4
Know which test you're facing — the preparation and timing are completely different.
Want to see how a specific drinking scenario translates to EtG levels? Use our EtG Calculator for a personalized estimate.
Related Reading
Medical & Legal Disclaimer
Not Medical Advice
EtGCalc does not provide diagnosis, treatment, or medical advice. Talk with a qualified healthcare provider about alcohol use, metabolism, testing concerns, or recovery.
Not Legal Advice
EtG testing can affect probation, custody, licensing, and employment decisions. Consult a licensed attorney or your testing program for legal questions.
If You Need Support
In the United States, SAMHSA's National Helpline is 1-800-662-4357. It is free, confidential, and available 24/7.
Calculator output is an estimate, not a test prediction. Individual metabolism, hydration, kidney function, genetics, specimen handling, and lab cutoff policy can change real results. See our methodology and sources.
References
- 1SAMHSA. The Role of Biomarkers in the Treatment of Alcohol Use Disorders, 2012 Revision.
Used for biomarker context, cutoff interpretation, and incidental exposure cautions.
- 2Jatlow et al. Ethyl glucuronide and ethyl sulfate assays in clinical trials, 2014.
Used for urinary EtG and EtS kinetics after alcohol exposure.
- 3McDonell et al. Using ethyl glucuronide in urine to detect alcohol use, 2015.
Used for EtG detection window context in clinical monitoring populations.
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