What a PEth level does — and doesn't — tell you.
PEth (phosphatidylethanol) is the blood test family courts rely on to show whether someone has been drinking over roughly the past two to four weeks. Whether you're deciding to order one or making sense of a result you already have, here's what it can prove, what it can't, and how to get a result that holds up in court — anywhere in the country.
How a PEth result is reported — and read
Your result comes back as a number measured in nanograms per milliliter (ng/mL) — your report may label it PEth 16:0/18:1. The clearest thing any report tells you is whether that number is negative or positive. Past that line, a higher number means less than most people expect.
| PEth level | How labs report it | What that does — and doesn't — tell you |
|---|---|---|
| Below ~20 ng/mL | Negative | Fits with not drinking — or with drinking too little, or too long ago, to reach the cutoff. A negative doesn't on its own prove zero drinking. |
| ~20 ng/mL and above | Positive | Shows that alcohol was in the body during the testing window. It doesn't show how much, how often, or on what day. |
A higher number generally reflects heavier or more sustained drinking — but only in a rough, general way, because people build up and clear PEth at very different rates. That is why a specific value cannot be turned into a specific amount, frequency, or date of drinking — and the limit cuts both ways: a high number does not prove a precise amount, and a low number does not rule out drinking.
Why you won't find a "what your level means" chart here.
Search for PEth online and you'll find charts that put a label on each number — this range means "social drinking," that one means "heavy drinking." We don't use one, and here's the honest reason.
Those charts come from research studies. In a study, the researchers already know how much each person drank and when — they decide it — and then they look at what PEth number shows up. Real life works the other way around: you have the number, and you're trying to figure out the drinking behind it. That doesn't work, because the same drinking shows up as very different numbers in different people. It's a little like a sunburn — the same hour in the sun leaves one person bright red and barely marks another, so you can't look at the burn and know exactly how long they were outside. In controlled studies, people who drank the exact same amount on the exact same schedule still came out with very different PEth numbers — several times higher in some people than in others. That's a real, measured effect, not a guess — so a single number simply can't tell you how much someone drank.
This is true of drug and alcohol testing in general, not only PEth. A test can show that alcohol was in the body during a window of time. It can't tell you how much a person drank, how often, or exactly when — the dose, the frequency, or the timing. The number is the end result; you can't run it backwards to work out what caused it. If someone reads a number as proof of how much or how often a person drank, or names the day it happened, they're claiming more than the test can actually show — and in a custody case, that's exactly the kind of claim that gets picked apart in court.
What the test does tell you is real and useful: whether alcohol was there, or not, during those weeks — backed by a clear, documented record of how the sample was handled from the moment it was collected. That record is what makes it hold up. What the number means for one particular person is a question for an expert brought in to answer it.
What PEth actually measures.
PEth forms inside your red blood cells only when alcohol is actually in your blood. No drinking, no PEth. That's what makes it one of the most reliable alcohol tests there is — it doesn't show up unless real alcohol was there.
Direct, not circumstantial
PEth only forms when you actually drink alcohol. It isn't triggered by hand sanitizer, mouthwash, kombucha, or fumes — so the "it wasn't really drinking" explanations that muddy other tests don't work here.
A pattern, not a snapshot
Because PEth builds up and clears slowly, one result reflects drinking across weeks — not the last few hours. It answers "has this person been drinking in recent weeks," not "were they drinking last night."
How far back a PEth test looks.
PEth can pick up drinking from roughly two to four weeks back — often up to about 28 days, and longer (up to a couple of months) after heavy or steady drinking. The more someone drinks, the higher the number and the longer it lasts. That long reach makes PEth the right tool for one kind of question — but not every question. There's no single "best" alcohol test; there's the one that fits the question you're asking.
| Test | Looks back roughly | The question it answers |
|---|---|---|
| Breath / blood alcohol | Hours | "Is there alcohol in their system right now?" |
| Urine EtG | Up to ~80 hours | "Was there drinking around a specific day or event?" |
| PEth (blood) | ~2–4 weeks | "Has there been drinking over the past few weeks?" |
Not sure whether your court order asks for PEth, EtG, or both? It matters — an order that names the wrong test, or sets a timing window that doesn't fit the test, can undo a perfectly good collection. See our guide to choosing the right family-court test, or call and we'll read the order with you. For a longer, multi-month history, hair testing covers months at a time.
Where PEth fits in a custody or monitoring case.
When the question is whether a parent has truly stayed off alcohol for weeks — not just been sober on test day — a long-reach test like PEth fits. Skipping alcohol the day before doesn't beat PEth the way it can beat a short-window test, and because PEth only forms from alcohol you actually drink, the "it was my mouthwash" answer doesn't apply. When the question is different — did someone drink around one specific day or event — a short-window test like EtG is the one that fits, because its narrow window ties the drinking to that moment. The order should name the test that fits the question being asked.
What matters as much as the test itself is the paper trail. A result only holds up in court if the sample's path — who collected it, when, and how it was sealed and handled — is written down with no gaps. That unbroken record (the "chain of custody") is what turns a lab number into evidence. It's also the line for what we'll speak to: how the sample was collected and what a result does and doesn't prove. Measuring the number is the lab's job; saying what it means for a particular person or case is a retained expert's.
What a PEth level can't tell you.
Reading a result honestly means knowing its edges. PEth is a strong test, but it is not a timeline and not a measure of amount.
It can't measure or date a drink
PEth reflects your drinking added up over recent weeks. It can't pin down when someone drank, how much, or on what day.
It doesn't measure being drunk
A PEth number says nothing about whether someone was drunk at any given moment. It's a look-back at past weeks, not a roadside sobriety check.
People clear it at different rates
The same number can mean different drinking in different people, because everyone builds up and clears PEth at their own rate. That's the main reason a number can't be read as a set amount — and why reading it is a retained expert's job.
Cutoffs and bands vary
The "positive" line at one lab can differ from another's, and there's no single agreed set of numbers that maps a level to an amount of drinking. Your lab's own cutoffs are the ones that count.
Getting a PEth test — here or anywhere in the country.
PEth is a blood test, usually a dried blood spot — a quick finger-stick onto a card — or a regular arm draw. Here's the part most people have backwards: the draw itself is the easy part. Drawing blood is routine. What decides whether a PEth result actually holds up is everything around the draw — the right test named in the order, an unbroken chain of custody (a documented record of how the sample was handled from start to finish), and a clear account of what the result does and doesn't prove. That's the part we're built for — and it's the same work whether you're down the street or across the country.
We collect at our Elk Grove Village office, and we can set up a court-ready PEth collection anywhere in the country through a nationwide collection network. Because the demanding part is the handling and documentation, not the draw, that value travels with it.
That nationwide reach isn't limited to PEth — the same applies to our other court testing, including hair testing (which is always collected in person by a trained collector). If your matter is court-related, our blood draw service is built for exactly this.
PEth questions, answered.
What is a normal PEth level?
US labs usually report PEth below about 20 ng/mL as negative — meaning no drinking, or too little to reach the cutoff — and positive at or above 20 ng/mL. A higher number roughly means heavier or steadier drinking, but there's no agreed set of numbers that turns a level into a set amount, and people clear PEth at very different rates. Your own report's cutoffs are what matter, and reading the number for your situation is a job for a retained expert.
Can a PEth level show how much, how often, or when someone drank?
No. A PEth result can show that alcohol was in the body during the testing window, but the number can't tell you how much a person drank, how often, or exactly when. The charts you'll see on some sites come from studies where the researchers already knew those things; in a real case it's the reverse — you have the number and not the drinking — and the same number can come from very different drinking in different people. Reading a number as a specific amount or date claims more than the test can show.
How far back does a PEth test detect alcohol?
Roughly two to four weeks — often cited as up to about 28 days — and longer, up to a couple of months, after heavy or steady drinking. The more someone drinks, the higher the number and the longer it stays detectable.
Is PEth a "binge-drinking" test — will one drink make me positive?
Very unlikely. PEth forms from any alcohol, but a single standard drink — one beer, one 5 oz glass of wine, or one shot — makes only trace amounts that stay below the 20 ng/mL positive cutoff. In controlled studies, even several drinks in one sitting after weeks of not drinking didn't cross it. What pushes PEth over the line is a real binge, or regular, repeated drinking over the weeks before the test. So an occasional standard drink won't read positive; a sustained pattern will.
Can hand sanitizer, mouthwash, or incidental exposure cause a positive PEth?
No. PEth only forms when you actually drink alcohol and it enters your blood. Alcohol you don't drink — mouthwash, hand sanitizer, fumes — doesn't create it, which is one of PEth's big advantages over some other alcohol tests.
Is PEth better than a urine EtG test?
Neither is "better" — they answer different questions. Urine EtG catches recent drinking over about the last few days and can tie it to a specific event; PEth shows drinking over the last few weeks and only reacts to alcohol you actually drink. Which one fits depends on your question and what your court order says — and some situations call for both.
What does a PEth level over 200 ng/mL mean?
A number this high usually means heavier or steadier drinking during the window, and some labs flag results above roughly 200 ng/mL as heavier use. But the same limit applies as at any level: it means more, not a set amount, and on its own it's not a diagnosis or a sign of being drunk. You can't work a number backward to how much or when someone drank, and reading it for a case is a retained expert's job.
Does TrueTest interpret my PEth result?
Not beyond what the laboratory itself reports. The lab analyzes the sample and publishes its own reference ranges — for example, flagging higher results as consistent with heavier use — and we'll walk you through what the lab and its cutoffs say. What your specific number means for your case, when it has to carry weight in court, is the retained expert's to deliver — and connecting you with the right one is part of what we do.
Need a PEth test that holds up?
Whether it's court-ordered or you just want a solid baseline, we'll collect it right, keep a documented record of how it was handled, and explain what the result does and doesn't prove.