Phencyclidine (PCP), commonly known as “angel dust,” is a dissociative anesthetic with powerful hallucinogenic effects. While drug testing identifies its presence, a positive result on an initial screen does not always mean PCP was used. This is known as a “false positive,” where a test indicates a substance is present when it is not. Though not the norm, these instances can arise due to various factors, leading to inaccurate readings.
Understanding False Positive Results
Drug tests, particularly initial screening tests, rely on a technique called immunoassay. This method works by detecting specific compounds or their metabolites in a sample, often urine, through the use of antibodies. These antibodies are designed to bind to the target substance, triggering a signal that indicates a positive result.
The challenge with immunoassay tests lies in their specificity. Sometimes, substances with chemical structures similar to the target drug, even if unrelated, can bind to these antibodies. This phenomenon, known as “cross-reactivity,” can lead to a false positive result. While initial immunoassay screens are quick and cost-effective, they are primarily qualitative, meaning they indicate presence rather than precise amounts, making them susceptible to these cross-reactions.
Common Medications and Their Impact
Several over-the-counter (OTC) and prescription medications have been documented to potentially cause false positive results for PCP due to cross-reactivity. These include:
- Antihistamines: Diphenhydramine, a common ingredient in allergy and sleep aids, and doxylamine, found in some sleep aids.
- Antidepressants: Serotonin-norepinephrine reuptake inhibitors (SNRIs) like venlafaxine and its metabolite desvenlafaxine.
- Cough suppressants: Dextromethorphan, often found in OTC cold medications.
- Pain medications: Tramadol, an opioid, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.
- Antipsychotics: Thioridazine and chlorpromazine.
Dietary Items and Medical Conditions
While many foods are known to cause false positives for other substances, such as poppy seeds for opiates, direct links between dietary items and false positives for PCP are not commonly reported. The chemical structures involved in PCP cross-reactivity are typically more complex than those found in common foods. Therefore, dietary intake is not a frequent cause of false positive PCP tests.
Certain medical conditions, however, can rarely contribute to false positive drug test results. Conditions affecting the body’s metabolism and excretion processes, such as liver disease or kidney disease, might alter how substances are processed and eliminated. This alteration could potentially lead to the accumulation of compounds that cross-react with immunoassay tests. While these occurrences are infrequent, they highlight the complex interplay between the body’s physiological state and drug test outcomes.
Navigating a False Positive Result
Receiving a false positive PCP test result can be concerning, but it is important to remember that initial screening tests are presumptive. If a preliminary test indicates a positive result, requesting a confirmatory test is the next step. The gold standard for confirmation is Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Mass Spectrometry (LC-MS).
These advanced analytical methods are highly specific and can accurately differentiate between PCP and other substances that might have caused a cross-reaction. When undergoing testing, it is advisable to disclose all medications, both prescription and over-the-counter, as well as any supplements or medical conditions, to the testing facility or healthcare provider. This information can help in interpreting the results accurately and can be particularly helpful if a confirmatory test is needed. Seeking legal or medical advice can also be beneficial if the situation has significant implications.