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Laboratories analyze drug metabolites primarily through chromatography (to separate compounds) coupled with mass spectrometry (to identify and quantify them). The process involves separating the mixture of metabolites using either gas chromatography (GC-MS) or liquid chromatography (LC-MS), followed by mass spectrometry to detect the mass-to-charge ratio of the ionized molecules, which confirms the identity and quantity of each metabolite. Other methods include radioactive labeling and nuclear magnetic resonance (NMR) spectroscopy.
Step-by-step analysis
Sample Preparation: A biological sample (like urine or blood) is collected, and sometimes prepared for analysis. For example, urine creatinine levels may be measured to normalize metabolite concentrations in the sample.
Chromatographic Separation: The sample is introduced into a chromatography system, where compounds are separated based on their chemical properties.
Mass Spectrometry (MS): The separated compounds are then sent to a mass spectrometer.
Identification and Quantification: The results from the mass spectrometer are analyzed to identify and quantify the metabolites present. The signal is proportional to the metabolite's concentration.
Confirmation: Because of the accuracy of techniques like LC-MS/MS and GC-MS, these are often used for confirmatory testing to rule out false positives from initial screening tests.
Alternative and complementary methods
Several types of drug tests use different biological samples to detect drug use over varying timeframes. Urine tests are the most common, while hair, saliva, blood, breath, and sweat tests are also used for specific purposes, such as detecting recent or long-term usage. The ideal test method depends on the reason for testing and the required detection window.
This is the most common and cost-effective drug testing method.
Detection window: Varies by substance, typically ranging from a few days to a week. For chronic marijuana users, it can be up to 30 days or longer.
Best for: Random drug testing, pre-employment screenings, and situations where a reasonable suspicion exists. It is most effective for detecting recent drug use.
Drawbacks: It is easier to tamper with a urine sample than with other collection methods.
Hair testing provides the longest detection window for drug use.
Detection window: Up to 90 days for most drugs. Because body hair grows slower, it may offer a longer detection window.
Best for: Identifying patterns of historical drug use and for pre-employment screening in safety-sensitive industries.
Drawbacks: More expensive and takes longer for results. It cannot detect very recent drug use, as it takes about a week for drug-laden hair to grow out of the scalp.
Also known as an oral fluid test, it involves collecting a sample with a mouth swab.
Detection window: Relatively short, typically between 24 and 48 hours for most substances, but longer for some drugs.
Best for: Detecting recent or current drug use, such as in post-accident or reasonable suspicion scenarios. The collection is simple, non-invasive, and observed, making tampering difficult.
Drawbacks: Shorter detection window and potentially lower accuracy for some substances compared to urine or blood tests.
This method requires drawing a blood sample from a vein.
Detection window: Very short, generally from minutes to hours, as drugs are quickly metabolized and eliminated from the bloodstream.
Best for: Medical emergencies, such as overdose situations, and for determining current impairment.
Drawbacks: It is the most invasive and expensive method, and the short detection window limits its utility for general screening.
Often used by law enforcement, it measures the level of alcohol in a person's breath.
Detection window: Detects recent alcohol consumption within a window of 12 to 24 hours.
Best for: Estimating blood alcohol concentration to determine current intoxication or impairment, especially at roadside checkpoints.
Drawbacks: Only tests for alcohol and has a very short detection window.
A patch worn on the skin collects sweat over a period of time.
Detection window: Provides a cumulative measure of drug use over several days to weeks.
Best for: Continuous monitoring, such as for individuals on parole or in rehabilitation programs.
Drawbacks: Potential for environmental contamination and is not as common as other methods.
**Urine testing is the best developed and most commonly used monitoring technique in substance abuse treatment programs. This appendix describes procedures for implementing this service and other methods for detecting clients' substance use. The Substance Abuse and Mental Health Services Administration (SAMHSA) has a number of documents about drug testing available in the Workplace Resources section of its Web site, www.samhsa.gov.
THC is absorbed into various body tissues and organs (e.g., the brain, heart, and in fat) or metabolized by the liver into 11-hydroxy-THC and carboxy-THC (metabolites). About 65% of cannabis gets excreted through feces and 20% leaves the body through urine.1 The rest is stored in the body.
Over time, THC that is stored in body tissues is released back into the bloodstream, where it is eventually metabolized by the liver.1 In chronic marijuana users, THC builds up in fatty tissues faster than it can be eliminated, so THC can also show up on a drug test many days or even weeks after an individual uses it.
THC, a highly fat-soluble compound, has a very long half-life—the amount of time it takes the concentration of THC in the body to decrease by half. How long residual THC levels remain in the body depends on an individual’s marijuana use. For example, one study found that the half-life was 1.3 days for individuals who infrequently used marijuana. More frequent use showed a half-life of somewhere between 5 and 13 days.
Additionally, detection of THC depends on the sample taken. Windows of detection vary.
