PEth levels: what the number can and can't tell you.

Your result comes back as a number, in nanograms per milliliter (ng/mL). Your report may label it PEth 16:0/18:1. The clearest thing it tells anyone is whether the result is negative or positive. Past that line, the number says less than most people expect.

The three ranges

Under 20

Fits with light drinking or no drinking. It is not proof of zero: occasional light drinking can stay under 20, drinking in the last few hours may not show yet, and some labs report down to 8 or 10 ng/mL.

200 and over

Generally considered heavy alcohol use. A level above 200 can't be reached from a single drinking episode. It takes more than one heavy drinking episode, or sustained drinking. The number can't say which — or how many drinks, or how often.

The gray area: 20–199

Published charts often put a drinking pattern on this range. The research doesn't support that. A PEth test can't tell you when someone drank, how much, or how often. Most charts are built from studies where the timing, amount and frequency of drinking were already known — and then read backward from the number, which the number can't do. A result here means drinking has occurred. Where it lands depends on things the number doesn't record:

• How recently the drinking stopped. PEth has a half-life: the level drops by half about every 4.5 days on average. That's an average — it can range from about 2 to 11 days.
• One episode or a longer pattern. One moderate drinking episode, or the tail end of heavier, sustained drinking that stopped several days earlier, can produce the same result.
• The person. Each body forms and clears PEth at its own rate.

Describing the drinking behind a middle-range number is a job for a retained expert with the full history, not a chart. That's why the number alone isn't enough — and why we walk you, your attorney or the GAL through what the report does and doesn't show.

What PEth measures

PEth forms inside red blood cells only when alcohol is actually in the blood. No drinking, no PEth. Hand sanitizer, mouthwash and fumes don't trigger it. Because it builds up and clears slowly, one result reflects drinking over roughly the past two to four weeks — not the last few hours. It answers "has this person been drinking in recent weeks," not "were they drinking last night."

A number is not a verdict

PEth is a record of drinking during its window. It does not show drinking on a specific day, or whether someone was drunk at a given moment. A high number does not prove a precise amount, and a low number does not rule out drinking.