Drug testing uses small samples of your blood, hair, saliva, or, most commonly, urine (pee). Drug tests can screen for a variety of drugs and their metabolites.
Depending on the test, it can cover everything from old standbys to new street drugs popular in raves and nightclubs. The accuracy of these tests varies by the method used.
Chemical Reactions
In general, drug tests screen for drugs or their metabolites in a biological sample, such as urine. Employers often require employees to provide a urine sample at a lab during pre-employment screening or when they reasonably suspect an employee is using illegal drugs. Hair, saliva (oral fluid), and sweat samples can also be tested for drug use. However, the most common type of drug test is a urinalysis.
Chemical reactions are a part of everyday life, including burning fuels, making pottery and glass, and brewing beer and wine. They rearrange the constituent atoms of the substances, known as reactants, to create different meanings called products with properties distinct from the original substances.
After a drug enters the body, the liver and other organs break it down into other chemicals, known as metabolites. The metabolites are then excreted, mainly through the urine—drug testing screens for metabolites of different types of drugs.
Random drug testing can reveal whether a person had used specific illegal substances but cannot show when or how much of the sense was consumed. Additionally, they cannot differentiate between short-term and long-term drug use, the appropriate use of medications, and their abuse. Moreover, employers who conduct random drug tests are policing private behavior unrelated to job performance.
Metabolites
Drug testing can check for metabolites or residues of drugs that remain in your system once the effects have worn off. Your body breaks down the chemicals from a substance into metabolites that are then excreted in urine, hair, saliva, and sweat.
During a drug test, specialists check these samples for the presence of the metabolites of certain drugs.
Your employer or physician can request a drug test for any reason. However, it is often used to detect substance abuse in safety-sensitive jobs like train engineers, airline pilots, and truck drivers. The worker provides a sample of their urine at a designated collection site. The selection is placed in a specially designed container and sealed with tamper-resistant tape. It then goes through a chain of custody to ensure the specimen is not tampered with or invalidated before it arrives at the laboratory.
At the lab, one aliquot of the sample is first screened with an immunoassay for the
presence of certain drugs. Some tests also check for pollutants that could have been added to the urine, such as oxidants, nitrites, and glutaraldehyde.
Gas chromatography-mass spectrometry (GC-MS) checks the resulting metabolites to confirm the initial findings. It should be noted that a positive result on a drug test does not indicate on-the-job impairment, nor can it determine the frequency or intensity of drug use.
Immunoassays
Immunoassay testing has been around for decades and is widely used in pharmaceutical drug discovery. Immunoassays measure the presence and
concentration of target analytes within a sample using a specific antigen-antibody reaction. If antibodies bind specifically to these compounds, they can detect drugs, metabolites, biomarkers, or small molecules.
Immunoassay methods are usually classified as competitive or non-competitive, depending on the type of interaction between antibody and analyte. Competitive immunoassays limit the number of antigen binding sites, forcing a labeled analyte and an unlabeled analyte to compete for the available binding sites. When the competition is over, the bound labeled analyte can be detected with a spectrophotometer or other instrument that measures the activity of the labeled analyte (e.g., a colorless chromogenic substrate or horseradish peroxidase). The resulting signal is directly proportional to the concentration of the analyte.
Non-competitive immunoassays use two antibodies that bind to distinct and non-overlapping epitopes on the analyte molecule, allowing for more precise detection. This design benefits large analytes with more than one recognition site on their molecule.
The extreme sensitivity of antibody-antigen interactions and the availability of instruments that enable automation have enabled high-throughput immunoassays to be developed, enabling a wide range of pharmaceutical drug discovery applications. For example, urine tests can screen for low molecular weight drug metabolites and other biomarkers in blood, urine, saliva, and cerebrospinal fluid (CSF). These tests are much faster and less expensive than chromatographic methods and require minimal samples.
Gas Chromatography-Mass Spectrometry
Gas chromatography-mass spectrometry (GC-MS) is a powerful analytical test that separates and identifies chemicals in liquid or volatile samples. This test uses two processes to provide the most accurate identification of analytes. The MS process fragments molecules into their components and then identifies them using a database or library of known spectra. The GC portion of this test separates the chemical mixtures into pulses of pure chemicals.
To perform a GC-MS analysis, the sample is first volatilized and swept through a specialized column by an inert carrier gas, such as nitrogen or helium. Based on their boiling point and polarity, the resulting compounds elute (or flow) from the column at different times. As the compounds pass through a heated transfer line into the mass spectrometer, they’re converted to ions. Once the ions are isolated, they can be identified by matching their m/z ratio to a database or library of known spectra.
Several mass spectrometry methods, such as electron impact (EI) or chemical ionization (CI), can be used during this process. Depending on the chosen method,
these techniques produce peak areas corresponding to different molecular weights, allowing chemists to identify a compound and its m/z ratio. GC-MS can be used to study liquid, solid and gaseous samples. Still, it’s most commonly applied in analyzing volatile substances such as drugs, solvents, fatty acids, and esters in food and cosmetics.