Donna asked
What would cause a positive for PCP?
Answer
There are a variety of drugs that have been reported to cause false-positives for PCP (phencyclidine) on standard urinalysis drug tests. These drugs include:
- Dextromethorphan: A common over the counter cough medication. It is the active ingredient in Delsym and is commonly included in combination ingredient cough/cold products such as NyQuil.
- Diphenhydramine: Diphenhydramine is the active ingredient in Benadryl, a sedating first-generation antihistamine used for allergies and insomnia.
- Ibuprofen: Ibuprofen is the active ingredient in Advil and Motrin. It is classified as an NSAID (non-steroidal anti-inflammatory drug) and is among the most commonly used over the counter analgesics.
- Imipramine: A tri-cyclic antidepressant, it is commonly used for depression, anxiety and as a sleep aid.
- Ketamine: Ketamine has a variety of uses but is commonly used as an analgesic and anesthetic.
- Meperidine: Meperidine is active ingredient in Demerol, a powerful opioid analgesic.
- Thioridazine: Classified as an atypical antipsychotic, thioridazine is often used for its sedative properties.
- Tramadol: Tramadol is the active ingredient in Ultram and is used for analgesia.
- Venlafaxine: Also known by the brand name Effexor, venlafaxine is a SNRI (serotonin norepinephrine reuptake inhibitor).
Why Do False Positives For PCP Happen?
Most drug testing labs use simple, urine based 'immunoassay' tests, such as the EIA (Enzyme Linked Immunoassay) test or the CEDIA (Closed Enzyme Donor Immunoassay) test. These tests work by utilizing antibodies to react to specific drug compounds (e.g. marijuana, PCP etc...). When a specified drug is present in a test urine sample, an antibody binds to it and produces a reaction. When a reaction occurs, it is classified as a 'positive' result.
Unfortunately, urine based immunoassay tests have a known problem with 'cross-reactivity'. Drugs that are NOT being tested for can occasionally react with the wrong antibody (i.e. 'cross react'), resulting in a 'false positive'. The list of drugs above (e.g. dextromethorphan, diphenhydramine etc...) have been known to cause false-positives for PCP.
If you believe you had a false-positive result for PCP, there are more accurate tests that can actually identify specific drug compounds, and don't rely on antibody reactions.
There are at least two tests available that can detect drug compounds in a specific manner:
- Gas chromatography-mass spectrometry (GC-MS)
- Hhigh-performance liquid chromatography (HPLC)
These tests do not use antibodies and can accurately determine the exact molecule in question. If you received a 'false positive', these tests will be able confirm whether or not the offending drug compound is present in the test sample. You can certainly inquire as to whether or not these tests are available to you in your situation.
