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Urine Phencyclidine (PCP) Screen

A yes-or-no urine test for PCP (phencyclidine). A positive is a first-step result, and several common medicines can cause false positives.

AI-verified against cited sources. Awaiting expert reviewAlso called PCPLOINC 19659-2

What it is

This urine screen checks for phencyclidine, known as PCP, an illegal drug. The result is negative or positive, not an amount. Labs use an immunoassay, a test built on antibodies that can also react to look-alike molecules. The cutoff is low, 25 ng/mL in federal workplace testing and at ARUP. PCP is on the federal workplace drug panel, and the screen is also used in emergency care, treatment programs and legal settings.

Why it matters

A positive screen can affect care, work, school or legal decisions, so it helps to know it is only a first step. Several common medicines, including a cough-medicine ingredient, can make a PCP immunoassay react. Labs therefore treat a positive as presumptive and often confirm it with a more specific test. A negative result means the test did not find PCP at or above the lab's cutoff. It does not prove none was taken.

If it’s high

A positive screen means the test reacted at or above the lab's cutoff. By itself it can't tell PCP use apart from a look-alike medicine. A confirmation test can usually sort this out, and several non-drug explanations are possible.

Common causes

  • A medicine that looks like PCP to the test, such as dextromethorphan, diphenhydramine, venlafaxine, tramadol, lamotrigine, imipramine or ibuprofen
  • Ketamine, which has also been reported to react
  • PCP use

What can help

  • Tell the clinician or reviewing physician about every prescription, over-the-counter medicine (including cough and cold products) and supplement you use
  • Ask whether the result will be confirmed with a more specific test
  • If you are worried about your own substance use, a clinician can talk through support options without judgment

What can affect your result

  • The lab's cutoff: the same sample can be negative on one test and positive on another
  • Medicines that look like PCP to an immunoassay
  • How long ago, how much and how often a substance was taken
  • Urine concentration: very dilute urine can push the level under the cutoff
  • Test type: immunoassay screens react to look-alikes, while mass spectrometry is more specific
  • Several common medicines have been reported to cause false-positive PCP screens, including dextromethorphan (in many cough and cold products), diphenhydramine, venlafaxine, tramadol, lamotrigine, imipramine, ibuprofen and ketamine.
  • The cutoff decides the answer. Federal workplace testing and ARUP's immunoassay both use 25 ng/mL, while Mayo's mass-spectrometry stimulant screen uses 20 ng/mL.
  • Very dilute urine can push the level under the cutoff and give a negative result.
  • A positive immunoassay is presumptive. Labs usually confirm it with a more specific method such as mass spectrometry.

A single random urine sample at any time of day. Some programs use an observed collection and check the sample for dilution or tampering. Reflects recent use. Drugs can be found from hours to several days or more after use, depending on the drug, the amount and how long it has been used.

When to talk to a clinician

A screen result is not an emergency by itself. Talk with your clinician about a positive result, especially if you take any of the medicines listed above. If you or someone else is confused, very agitated, unable to be calmed, or has seizures, chest pain or trouble breathing after taking a drug, call 911 or your local emergency number.

Questions you could ask

  • Which cutoff did this test use?
  • Who will see this result, and how will it be used?
  • Will this result be confirmed with a more specific test?
  • Could any of my medicines, including cough or cold products, explain this result?

Questions people ask

Can cough medicine cause a positive PCP test?

It can. Dextromethorphan, an ingredient in many cough and cold products, is among the medicines reported to cause false-positive PCP screens. Tell the person reviewing your result about every medicine you take, including over-the-counter ones.

Does a positive PCP screen mean I used PCP?

Not on its own. A screen is a first step, and a confirmation test is how labs tell PCP from look-alike substances. If the result surprises you, ask for confirmation and share your medicine list.

Why do labs use different cutoffs?

A cutoff is the level at which the lab calls a screen positive. Federal workplace testing and ARUP use 25 ng/mL, and Mayo's mass-spectrometry screen uses 20 ng/mL. A lower cutoff catches smaller amounts, so the same sample can read differently at two labs.

Show the science and sources

For clinicians and researchers

PCP screening is an immunoassay with a low cutoff. The HHS federal workplace urine panel (effective February 2024) uses 25 ng/mL for both the initial test and confirmation. ARUP's clinical immunoassay panel also uses 25 ng/mL and reflexes positives to mass-spectrometry confirmation. Mayo's LC-MS/MS stimulant screen reports PCP at 20 ng/mL. LOINC has separate codes for screens defined by a 25 ng/mL cutoff, and for 20 ng/mL confirmation. PCP is one of the five drug classes required in federal workplace testing (Moeller 2008). False-positive PCP immunoassays are reported with a long list of agents. A 2023 case report describes a likely false positive in a 17-year-old on long-term therapeutic venlafaxine, and notes literature reports with dextromethorphan, ibuprofen, imipramine, diphenhydramine, ketamine, lamotrigine and tramadol (Kim 2023). Immunoassay cross-reactivity varies by manufacturer, so any list of interferents is assay specific. Positive immunoassays are considered presumptive until confirmed by a second, independent technique (Saitman 2014).

LOINC 19659-2 (primary), 113587-0, 3936-2, 8238-8, 14310-7, 18392-1. Specimen: urine.

Sources

  1. Mandatory Guidelines for Federal Workplace Drug Testing Programs Using Urine Specimens, 88 FR 70768, U.S. Department of Health and Human Services (SAMHSA), Federal Register (2023)
  2. Drug Panel 7, Urine - Screen with Reflex to Confirmation/Quantitation (test 0092184), ARUP Laboratories
  3. Controlled Substance Monitoring Hybrid Drug Profile, 20 Drug Classes, High-Resolution Mass Spectrometry and Immunoassay Screen, Random, Urine (CSMHU), Mayo Clinic Laboratories (catalog mirror at testcatalog.org)
  4. Drug Testing, MedlinePlus (U.S. National Library of Medicine)
  5. False-Positive Phencyclidine (PCP) Result on 11-Panel Urine Drug Screen (UDS) in a 17-Year-Old Adolescent with Long-Term Venlafaxine Use, Case Reports in Psychiatry 2023 (2023)
  6. Urine drug screening: practical guide for clinicians, Mayo Clinic Proceedings 2008;83(1):66-76 (2008)
  7. False-positive interferences of common urine drug screen immunoassays: a review, Journal of Analytical Toxicology 2014;38(7):387-396 (2014)
  8. LOINC codes verified with the NLM Clinical Tables LOINC search, U.S. National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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