USDTL resource guide
PEth blood testing
Phosphatidylethanol
An alcohol-specific blood marker that offers a view over the preceding weeks.
The approximate testing window
A visual reference for this specimen.
Approximate window, not guaranteed detection or clearance. The bar shows a general span, not continuous coverage or a probability. Shaded ends represent the stated range. Review the limitations and sources below. View sources.
What this test tells you
PEth forms in the presence of alcohol and is incorporated into red blood cell membranes. USDTL describes detection up to approximately two to four weeks, with isolated cases lasting six weeks or longer.
What collection involves
USDTL accepts dried blood spots and whole blood collected by venipuncture. Confirm which specimen the order requires.
Keep in mind
A PEth result does not establish current intoxication or an exact drinking date. Detection varies by person and use pattern.
A common question
Is PEth the same as CDT?
No. PEth is a direct alcohol biomarker. CDT measures a change in transferrin and requires different clinical interpretation.
Read the original resources.
Source material behind this guide.
- USDTL · PEth and dried blood spot testingBlood specimens and the variability of PEth detection.
- USDTL · Made in the bloodAlcohol biomarkers and limitations of urine and hair testing.
Reviewed October 26, 2026. Laboratory guidance can change; the current order and report take priority.