The abbreviation “AMP” on a drug test refers to amphetamines, a class of powerful central nervous system stimulants. Amphetamine testing is a standard component of most panel screens, routinely used for pre-employment, legal, and medical monitoring. While the primary goal is to detect illicit substances, the test also screens for legally prescribed medications in this chemical category. The initial screening is highly sensitive but not entirely specific, meaning a positive result does not automatically confirm illegal drug use. Accurate interpretation requires understanding the difference between the intended targets and other substances that can interfere with the test.
The Core Targets of the Amphetamine Panel
The amphetamine panel detects compounds sharing the phenethylamine structure. This includes the parent drug, amphetamine, often prescribed for conditions like ADHD and narcolepsy; medications like Adderall will trigger a positive result. Methamphetamine, a more potent compound known as crystal meth, is another primary target. The body metabolizes methamphetamine into amphetamine, so a positive result for both often indicates methamphetamine use. The panel also detects designer drugs like 3,4-methylenedioxymethamphetamine (MDMA), or Ecstasy, and its metabolite, MDA.
How Drug Screening and Confirmation Tests Work
Drug testing follows a two-step process to ensure accuracy. The initial screen uses an immunoassay (IA) technique, which is fast and inexpensive. This method utilizes antibodies designed to bind to the drug or its metabolites above a predetermined concentration threshold.
The immunoassay is highly sensitive to minimize false negatives, but this comes at the cost of specificity. Antibodies can cross-react with other compounds structurally similar to amphetamines. A positive immunoassay result is considered a presumptive positive, necessitating a second, more definitive step.
The confirmatory test uses sophisticated technology, usually Gas Chromatography-Mass Spectrometry (GC/MS) or Liquid Chromatography-Mass Spectrometry (LC-MS/MS). This technique separates the sample into its chemical components, identifying the exact molecular fingerprint of any substance present. These methods are the gold standard because they are highly specific and accurately distinguish amphetamine from chemically similar compounds, ruling out false positives.
Common Medications That Cause False Positives
A significant number of legally available medications and over-the-counter products can result in a presumptive positive for amphetamines on the initial immunoassay screen. This occurs due to chemical cross-reactivity, where the antibodies in the test mistake a non-amphetamine molecule for the target drug. Several common medications are structurally similar to amphetamines and frequently trigger false positives:
- Antidepressants like bupropion (used for depression and smoking cessation) and sertraline.
- Over-the-counter cold remedies containing decongestants such as pseudoephedrine and ephedrine.
- The cough suppressant dextromethorphan and certain antihistamines like brompheniramine.
- The weight-loss stimulant phentermine.
- Certain beta-blockers (e.g., labetalol) and the antacid ranitidine.
If a person is taking any of these medications, the initial screening result must be viewed with caution until a confirmation test is performed.
Necessary Steps Following a Positive Screening
If an initial immunoassay screen returns a presumptive positive result for amphetamines, the process mandates the involvement of a licensed physician known as a Medical Review Officer (MRO). The MRO acts as an independent gatekeeper, determining if a legitimate medical explanation exists for the non-negative test result. The MRO initiates confidential contact with the individual, typically making at least three attempts within a 24-hour period.
During this interview, the MRO asks the donor to provide documentation, such as valid prescriptions or medical records, to explain the substance’s presence. If the donor confirms using a medication known to cause cross-reactivity, the MRO orders the confirmatory GC/MS or LC-MS/MS testing. If the confirmatory test verifies the substance is a legitimately taken prescription medication, the MRO reports the final result to the employer as negative. This crucial step protects the individual, ensuring that legal and prescribed medication use is not misinterpreted as illicit drug use.