Alcohol Metabolites: What They Are

When a person drinks ethanol (alcohol), the body breaks it down in the liver. Most is metabolized to acetaldehyde → acetic acid, but some minor metabolites are formed that are direct markers of alcohol exposure. These include:

• EtG (Ethyl Glucuronide): Formed when ethanol combines with glucuronic acid.

• EtS (Ethyl Sulfate): Formed when ethanol combines with sulfate.

• PEth (Phosphatidylethanol): Formed in red blood cell membranes when ethanol reacts with phospholipids.

• FAEEs (Fatty Acid Ethyl Esters): Formed when ethanol combines with fatty acids (incorporates into hair).

Unlike ethanol itself (which is gone in hours), these metabolites stay in body fluids/tissues longer and are used for testing.

How They Are Measured

• Urine: EtG/EtS measured by LC-MS/MS (liquid chromatography–tandem mass spectrometry).

• Blood: PEth measured by LC-MS/MS.

• Hair/Nails: EtG or FAEEs measured in washed and extracted samples via LC-MS/MS or GC-MS.

• Saliva/Breath: Direct ethanol detection (not metabolites).

Cutoffs & Interpretation

(Note: Cutoffs vary slightly by lab; these are the most widely cited / consensus ranges from SAMHSA, SoHT, and forensic guidelines.)

1. Urine EtG / EtS

• Common Screening Cutoffs:

  • EtG: 500 ng/mL (forensic/clinical use; SAMHSA guideline)

  • Some labs use 100–200 ng/mL for research or recovery monitoring, but this risks false positives from incidental exposure (mouthwash, hand sanitizer).

• Detection Window: ~1–3 days after drinking.

• Use: Detects recent drinking, not chronic use.

2. Blood PEth

• Cutoffs:

  • 20 ng/mL = positive (any alcohol exposure).

  • 20–200 ng/mL = moderate/repeated use.

  • >200–250 ng/mL = chronic heavy use (commonly accepted forensic threshold).

• Detection Window: ~2–4 weeks, longer with heavy/frequent drinking.

• Use: Strong marker of chronic/frequent drinking.

3. Hair EtG / FAEE

• EtG Cutoffs (Society of Hair Testing – SoHT):

  • ≥30 pg/mg = indicates repeated or chronic excessive drinking.

  • <7 pg/mg = consistent with abstinence or very low intake.

  • 7–30 pg/mg = gray zone; interpretation depends on context.

• FAEE Cutoffs (in hair):

  • ≥0.5 ng/mg (500 pg/mg) = excessive drinking.

• Detection Window: ~90 days per 3 cm segment of hair (3 months).

• Use: Best for chronic excessive use, not occasional drinking.

4. Nail EtG

• Cutoffs: No universal standard, but labs often use ≥30 pg/mg (mirroring hair).

• Detection Window: ~3–6 months.

• Use: Similar to hair, but slightly longer window.

5. Oral Fluid / Breath

• Oral Fluid (Saliva): Detects parent ethanol, not metabolites.

  • Cutoff: ~20 µg/dL (varies by device).

  • Window: 12–24 hours.

• Breathalyzer:

  • Cutoff for impairment (U.S. legal): 0.08% BAC (80 mg/dL).

  • Detection Window: Only during intoxication.