Understanding the difference between EtG, EtS, and BAC helps you read test results correctly and avoid common misconceptions.
Quick definitions
- BAC (Blood Alcohol Concentration): How much ethanol is in your blood right now. It rises during/after drinking and usually drops to zero within hours.
- EtG (Ethyl Glucuronide): A direct metabolite of ethanol, measured mostly in urine. Can be detectable after BAC returns to 0.
- EtS (Ethyl Sulfate): Another ethanol metabolite, often tested with EtG to reduce false positives and improve confidence.
Key takeaway: BAC ≠ EtG/EtS. A person can have a BAC of 0 and still test positive for EtG/EtS.
Typical specimen & window
| Marker | Common specimen | Typical window (urine) | What it’s used for |
|---|---|---|---|
| BAC | Breath/Blood | Hours | Current or very recent drinking |
| EtG | Urine | ~12–96 h* | Recent drinking over last 1–4 days |
| EtS | Urine | ~12–96 h* | Confirmatory alongside EtG |
* Wide range. Dose, timing, physiology, hydration, and lab cutoff strongly affect the window.
Why labs measure both EtG and EtS
- Confirmatory value: Measuring both metabolites helps validate true positives.
- Stability differences: EtS is generally more stable; together they provide a clearer picture.
Cutoffs matter
Lower cutoffs (e.g., 100 ng/mL) can detect longer than higher cutoffs (e.g., 500 ng/mL). Programs and clinics choose cutoffs based on goals and policies.
Frequently asked
Can BAC be zero while EtG/EtS are positive? Yes. BAC falls quickly; metabolites can remain for days.
Do mouthwash or incidental exposures cause positives? Policies vary. Labs often consider the overall pattern and may use EtS and creatinine correction to interpret results more reliably.
FAQ
Q: How long after drinking can EtG and EtS be detected? A: Typically 12-96 hours in urine, depending on amount consumed, individual factors, and lab cutoff levels. EtG/EtS last much longer than BAC.
Q: Why do some tests measure both EtG and EtS together? A: Testing both metabolites increases accuracy and reduces false positives. EtS is more stable than EtG, so together they provide better confirmation of alcohol consumption.
Q: Can I have a positive EtG test if my BAC is 0.00? A: Absolutely. BAC measures current alcohol in blood and drops to zero within hours. EtG/EtS are metabolites that remain detectable for days after BAC returns to zero.
Q: Do different labs use different cutoff levels? A: Yes. Common cutoffs are 100, 200-300, or 500 ng/mL. Lower cutoffs (100 ng/mL) detect alcohol for longer periods than higher cutoffs (500 ng/mL).
Q: Can hand sanitizer or cooking wine cause a positive EtG test? A: Small incidental exposures typically don’t cause positive tests at standard cutoffs, but policies vary by program. Labs often look at the overall pattern and EtS levels for interpretation.
Q: How accurate are EtG/EtS tests? A: Very accurate when interpreted correctly. False positives are rare at appropriate cutoffs, and testing both metabolites together increases reliability.
Disclaimer
This article is for educational purposes only and does not provide medical, legal, or employment advice.