A drug screen is a specialized test designed to detect the presence of specific substances or their byproducts, known as metabolites, in a biological sample like urine or saliva. These laboratory reports often rely on abbreviations to categorize the substances being tested, which can make the results confusing for the average person. The use of shorthand allows testing facilities to maintain efficiency when processing a high volume of samples. This article clarifies the specific meaning and implications of the abbreviation “MET” when encountered on a drug screen.
Decoding MET: Identifying the Substance
The abbreviation MET on a drug screen report universally stands for Methamphetamine, a potent synthetic stimulant that affects the central nervous system. This substance is classified as a sympathomimetic amine, meaning it mimics the effects of the body’s natural adrenaline-like hormones. Methamphetamine is a Schedule II controlled substance, recognized for its high potential for abuse and dependence.
Once ingested, the body’s metabolic processes begin to break the parent drug down into other compounds. The primary metabolite of methamphetamine is amphetamine, which is also a psychoactive stimulant. A comprehensive drug screen is designed to detect both the parent drug, methamphetamine, and this active metabolite, amphetamine, to ensure accurate identification of use.
Laboratories may report the results for methamphetamine and amphetamine separately, or they may group them under a single MET or AMP/MET category. The presence of both parent drug and metabolite helps to differentiate illicit use from the use of other chemically similar, but legally prescribed, medications.
The Initial Screen and Cut-Off Levels
The process of drug testing begins with an initial screening test, which is most often performed using an immunoassay method. This technique is favored by laboratories because it is a rapid, cost-effective way to process a large number of samples quickly. Immunoassays work by using antibodies designed to bind to the specific drug or its metabolites in the collected sample.
The result of this initial screen is a preliminary determination based on a pre-established threshold called the cut-off level. This cut-off level is a minimum concentration, expressed in nanograms per milliliter (ng/mL), that the drug or metabolite must meet or exceed to be flagged as positive. For methamphetamine screening in urine, common cut-off levels are either 500 ng/mL or 1000 ng/mL, depending on the testing program and regulatory standards.
The cut-off level helps to distinguish between actual substance use and incidental exposure. If the concentration of methamphetamine or its metabolite is below this pre-set threshold, the result is reported as negative. Conversely, any concentration equal to or above the cut-off level triggers a preliminary positive result.
This preliminary positive result is only a presumptive finding, not a final confirmation of drug use. The immunoassay method, while fast, can sometimes suffer from cross-reactivity, where antibodies mistakenly bind to compounds that are chemically similar to the target drug. For example, certain over-the-counter cold medicines can potentially cause a preliminary positive result on an amphetamine screen. Therefore, any non-negative result from the initial screen must proceed to a more rigorous confirmation process to ensure accuracy.
Confirmation Testing and Final Result Interpretation
When a drug screen yields a presumptive positive result for MET, the sample is automatically subjected to a confirmation test to verify the initial finding. This second stage of testing is necessary because the initial immunoassay is not specific enough to be legally or medically definitive. The gold standard for this confirmatory analysis is a technique called Gas Chromatography/Mass Spectrometry (GC/MS) or Liquid Chromatography/Mass Spectrometry (LC/MS).
These mass spectrometry methods are highly precise, functioning as a definitive molecular fingerprinting process. The instrument first separates the various chemical components within the urine sample and then analyzes their molecular weight and fragmentation pattern. This allows the mass spectrometer to unequivocally identify and quantify the exact drug compound and its metabolites present in the sample.
Confirmation testing provides a final, legally defensible result, which is crucial in employment, forensic, or clinical settings. GC/MS has the capability to differentiate between the two chemical forms, or isomers, of methamphetamine: d-methamphetamine and l-methamphetamine. The d-isomer is the more potent, commonly abused form, while the l-isomer can be found in some over-the-counter nasal decongestants.
The confirmation test applies its own, often lower, cut-off level, which must be exceeded for the result to be reported as a confirmed positive. Final interpretation of the result also considers factors like a sample’s creatinine level and specific gravity, which can indicate if the sample was diluted. A confirmed positive means that methamphetamine or its metabolite was definitively identified at a concentration above the final cut-off.