A PEth test is a blood draw that can pick up alcohol use from roughly the last two to four weeks, while an EtG test is a urine test that generally only reflects drinking from the last one to three days. Both are lab-based biomarker tests a program orders through a laboratory, not instant on-site screens. If you need a same-day read at the point of collection, that job belongs to a breathalyzer, saliva alcohol screen, or alcohol test strip, with PEth or EtG ordered afterward when a longer look-back window or confirmation-grade result is needed.
What PEth and EtG actually measure
PEth (phosphatidylethanol) and EtG (ethyl glucuronide) are both "direct" alcohol biomarkers, meaning they form in the body specifically when ethanol is present, unlike indirect markers such as liver enzymes that can be elevated for many reasons. According to the Substance Abuse and Mental Health Services Administration's advisory on alcohol biomarkers, PEth is a serum-based biomarker whose persistence in blood can extend to as long as three weeks after even a few days of moderately heavy drinking, and the same advisory's summary table lists PEth's return-to-normal window with abstinence at two to four weeks. EtG, by contrast, is measured in urine and the same SAMHSA advisory notes it may become positive after perhaps as little as a single drink and typically remains detectable for one to two days after low-level exposure, with the advisory's summary table listing EtG's return-to-normal window at one to three days.
That gap in detection windows is the core reason programs choose one test over the other. PEth's multi-week window makes it useful for confirming sustained abstinence over time. EtG's short window makes it useful for verifying that a specific recent period, such as the day before a scheduled appointment or the days since a last check-in, was alcohol-free.
EtG's sensitivity is also its limitation
Because EtG can register a positive from very small amounts of ethanol, it is sensitive to incidental exposure through products that are not beverage alcohol, including some mouthwash, hand sanitizer, cosmetics, and foods prepared with alcohol. SAMHSA's advisory specifically cautions that EtG and EtS results should not be used as the sole basis for high-stakes decisions without accounting for this incidental-exposure risk. That does not make EtG a poor test, but it does mean a positive result should prompt a conversation and, where appropriate, confirmation testing and clinical judgment rather than an automatic conclusion.
Where DOT-regulated alcohol testing fits in
It is worth separating DOT compliance testing from clinical or program-based biomarker testing, because they are not the same thing. Under 49 CFR Part 40, the alcohol screening test and confirmation test that DOT-regulated employers must use are performed with an approved breath device or, for screening only, a saliva device. Part 40's own definitions describe an alcohol screening device as a breath or saliva device and an alcohol confirmation test as a subsequent test using an evidential breath testing device. Urine EtG and blood PEth are not part of the DOT-regulated alcohol test itself. Where PEth or EtG do show up in a DOT context is on the treatment and monitoring side. A substance abuse professional's return-to-duty and follow-up plan for an employee who violated a DOT alcohol regulation can call for its own monitoring approach, which may include lab-based biomarkers, but that sits alongside the Part 40 test rather than replacing it. Employers building a return-to-duty or treatment-adjacent monitoring plan should confirm with their SAP or MRO which tests apply to which part of the process.
Where instant alcohol screening fits before you ever order a lab biomarker
Most workplace and program alcohol testing does not start with a lab order. It starts with an instant, on-site device that gives a result in minutes: a breathalyzer, a saliva-based alcohol screen, or an alcohol test strip. These devices answer a different question than PEth or EtG do. A breathalyzer or saliva screen tells you whether alcohol is present right now, at the moment of testing, which is exactly what a random test, a reasonable-suspicion check, or a post-accident protocol needs. PEth and EtG answer a longer-range question: has this person had any drinks over the past several days to several weeks. Programs that need both answers typically use the instant device for same-day decisions and reserve the lab-based biomarker for periodic verification or for cases that need a documented, longer look-back. For addiction recovery and treatment settings specifically, that combination often looks like routine on-site alcohol test strips or saliva screens between visits, backed by a lab-ordered PEth or EtG at scheduled intervals to catch anything the spot checks missed. ASC's addiction recovery and drug and alcohol testing collection is built around that kind of layered program, and its DOT drug and alcohol testing collection for transportation companies covers the breath and saliva devices that satisfy Part 40 screening on the compliance side.
PEth vs EtG vs breath vs saliva
| Method | Specimen | What it detects | Typical detection window | Best used for |
|---|---|---|---|---|
| Breathalyzer | Breath | Current breath alcohol concentration | Current use, a matter of hours | Real-time impairment checks; DOT-required confirmation test under Part 40 |
| Saliva alcohol screen / alcohol test strip | Saliva | Current or very recent alcohol presence | Current to same-day use | On-site screening before a lab referral; DOT-permitted screening device |
| EtG | Urine (lab-ordered) | Direct alcohol metabolite | About 1 to 3 days per SAMHSA's advisory | Short-window abstinence verification; probation, court, and treatment check-ins |
| PEth | Blood (lab-ordered) | Direct alcohol biomarker on red blood cells | About 2 to 4 weeks per SAMHSA's advisory | Longer-range abstinence monitoring; treatment program compliance; return-to-duty aftercare |
Choosing between PEth and EtG for a program
A few practical questions tend to settle which lab biomarker fits a given program:
- How far back do you need to look? If the goal is confirming several weeks of abstinence, PEth's longer window does more work per test. If the goal is verifying the last day or two, EtG is the closer match.
- How much does incidental exposure risk matter in this setting? EtG's sensitivity to non-beverage alcohol sources means results benefit from a conversation with the individual and, where the stakes are high, confirmation testing.
- What does the receiving party expect? Courts, probation departments, treatment programs, and workplace SAPs each tend to have established preferences; check with the ordering laboratory or MRO before building a protocol around either test.
- What sits between lab draws? This is where instant alcohol test strips, saliva screens, and breathalyzers come in, giving a program same-day visibility on the days it is not sending a specimen to a lab.
Frequently asked questions
What is the main difference between a PEth test and an EtG test?
A PEth test is a blood draw that detects an alcohol biomarker formed only in the presence of ethanol, with a detection window of roughly two to four weeks. An EtG test is a urine test for a direct alcohol metabolite that generally returns to baseline within about one to three days after drinking stops, per SAMHSA's alcohol biomarkers advisory.
Can an EtG test come back positive from mouthwash or hand sanitizer?
Yes. Because EtG is highly sensitive, exposure to alcohol in mouthwash, hand sanitizer, cosmetics, and some foods can produce a positive result without beverage alcohol consumption, which is why SAMHSA advises against using an EtG result alone to make high-stakes decisions.
Does DOT drug and alcohol testing use PEth or EtG?
No. Under 49 CFR Part 40, the DOT-regulated alcohol test itself is performed only with an approved breath or saliva device, not urine EtG or blood PEth; those biomarkers may appear separately in a substance abuse professional's aftercare monitoring plan.
Which test is better for monitoring long-term abstinence?
PEth is generally preferred for longer-range abstinence monitoring because its two to four week window catches drinking episodes that a one to three day EtG window would miss between test dates.
Where do instant alcohol screening devices fit alongside PEth and EtG?
Breathalyzers, saliva alcohol screens, and alcohol test strips give an immediate, on-site read at the moment of testing, while PEth and EtG are lab-based tests a program orders through a laboratory when it needs a longer look-back window or confirmation-grade documentation.
Do PEth and EtG results require confirmation?
Any non-negative screening result should be treated as presumptive and handled according to your program's confirmation and medical review procedures, not as a final determination on its own.
Related reading
For more on how urine-based alcohol metabolite testing works on its own, see ASC's guide, What to Know About EtG Testing, and for a closer look at breath, saliva, and EtG side by side, see Workplace Alcohol Testing Methods: Breath, Saliva, and EtG Compared.
This article is for general informational purposes and is not medical, legal, or compliance advice. PEth and EtG are screening and monitoring tools; they support but do not replace clinical judgment, laboratory confirmation, and medical review officer procedures. Program design should follow guidance from your laboratory, medical review officer, substance abuse professional, or legal counsel as applicable.
