Drug tests in forensic laboratories are conducted to detect, identify, and quantify drugs or their metabolites in biological samples such as blood, urine, hair, or saliva. These tests are essential for criminal investigations, workplace testing, and toxicology analysis. Here’s how they are generally conducted:
1. Sample Collection
- Samples are collected from the suspect or victim, often blood, urine, hair, saliva, or tissue.
- Proper handling and labeling are crucial to maintain the chain of custody and prevent contamination.
2. Initial Screening
- The first step is usually a screening test to check for the presence of drugs.
- Common techniques:
- Immunoassays: Use antibodies that react with specific drugs (e.g., ELISA).
- Colorimetric tests: Simple chemical tests that produce a color change when a drug is present.
- Screening tests are quick and sensitive but may produce false positives.
3. Confirmatory Testing
- Positive results from screening are confirmed using more precise and reliable methods.
- Techniques include:
- Gas Chromatography–Mass Spectrometry (GC-MS): Separates and identifies drug molecules with high accuracy.
- High-Performance Liquid Chromatography (HPLC): Measures drugs in biological fluids, especially non-volatile or heat-sensitive compounds.
- Liquid Chromatography–Mass Spectrometry (LC-MS/MS): Highly sensitive, used for detecting very small drug amounts and metabolites.
4. Quantification
- Once the drug is identified, its concentration is measured.
- Quantification helps determine:
- Whether the drug was at therapeutic, toxic, or lethal levels.
- The time and amount of drug intake in some cases.
5. Specialized Testing
- Hair analysis: Can detect drug use over several months.
- Saliva testing: Provides information about recent drug intake.
- Tissue or postmortem samples: Used in forensic toxicology to determine cause of death.
6. Documentation and Reporting
- All results are carefully recorded with supporting chromatograms, spectra, or test data.
- Forensic chemists provide a report that can be used in court as evidence.
- Expert testimony may explain the testing process and results to judges and juries.
Key Points
- Drug testing in forensic labs follows a two-step process: screening for quick detection and confirmatory testing for accuracy.
- GC-MS and LC-MS are considered the gold standard for confirmatory drug analysis.
- Maintaining sample integrity and following strict lab protocols is essential for legal validity.