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Drug monitoring, Phoshatidylethanol (PEth), Blood Test

Test Code: 12198

Phosphatidylethanol (PEth) is an abnormal phospholipid formed in the presence of ethanol (more commonly known as alcohol). PEth binds to the membranes of red blood cells.

There are 48 known homologs of PEth in the blood.1 The most common include:

  • PEth 16:0/18:1 (POPEth): The predominant homolog accounting for ~37% of total PEth in blood.
  • PEth 16:0/18:2 (PLPEth): A major homolog accounting for ~26% of total PEth in blood

The pharmacokinetics of PLPEth differ from POPEth.

A phosphatidylethanol (PEth) blood test measures the level of PEth, an alcohol biomarker found in blood after alcohol consumption. PEth is a more direct indicator of alcohol consumption than other alcohol biomarkers (eg, ethyl glucuronide [EtG]/ethyl sulfate [EtS]) that may be formed from incidental sources containing alcohol (eg, hand sanitizers).1

PEth testing may also provide a longer window of detection (eg, 1-2 weeks) than EtG and EtS (e.g., 80 hours). PEth may be detectable for extended periods (eg, 4 weeks) in chronic/excessive alcohol users.1,2 Higher alcohol consumption leads to higher PEth levels in the blood. Testing for PEth may be useful as a baseline test for identifying alcohol consumption in new patients, transplant candidates, post-transplant recipients, and patients who have not been monitored recently.

PEth testing can be performed on patients who may have difficulty providing a urine specimen (eg, transplant patients).

The PEth test order code is 12198. Measurement is done by LC-MS/MS.

Test code 12198 is currently being performed at Quest Diagnostics Nichols Institute, Chantilly Laboratory.

Sample collection for this test is via standard blood draw. Specimens can be collected in office or at a local Quest Patient Service Center.


  • The preferred specimen type is whole blood collected in an EDTA (lavender-top) tube, minimum volume 0.5 mL

Stability requirements

  • Room temperature: 5 days
  • Refrigerated: 30 days
  • Frozen: 30 days

Rejection criteria

  • Non–whole blood samples
  • Non-EDTA (lavender-top) tube

The PEth test results include 2 components that may indicate probable abstinence or probable chronic drinking and confirm the presence of PEth:

16:0/18:1 (POPEth)

  • <20 ng/mL: probable abstinence1
  • >200 ng/mL: probable chronic drinking1

16:0/18:2 (PLPEth)

  • Confirms presence of PEth
  • Does not have established reference ranges1; subject to change as more data become available

A PEth test may not detect a single drink or casual drinking. A negative result is not always indicative of abstinence.  A positive result may indicate chronic drinking (multiple drinks/day).1

Yes. PEth testing is considered a clinical test; therefore, multiple clinical specimens from one patient may be placed in the same bag. However, specimens from another patient should be placed in a separate bag. 

For any questions regarding this information or assistance with interpreting these drug test results, please contact a Quest toxicology specialist at 1.877.40.RX TOX (1.877.407.9869). Specialists are available to assist Monday through Friday from 8 AM to 10 PM ET.


  1. Ulwelling W, Smith K. The PEth blood test in the security environment: what it is; why it is important; and interpretative guidelines. J Forensic Sci. 2018;63(6):1634-1640. doi:10.1111/1556-4029.13874
  2. Schröck A, Pfäffli M, König S, Weinmann W. Application of phosphatidylethanol (PEth) in whole blood in comparison to ethyl glucuronide in hair (hEtG) in driving aptitude assessment (DAA). Int J Legal Med. 2016;130(6):1527-1533. doi:10.1007/s00414-016-1394-4


This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.



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