Toxicological Screen
Definition
A systematic analysis of biological specimens for drugs, poisons, or their metabolites. Typically a two-stage process: an immunoassay screen followed by a chromatography-mass spectrometry confirmation.
- Stage 1
- Immunoassay screen
- Stage 2
- GC-MS or LC-MS/MS confirmation
- Purpose
- Detect drugs, poisons, or their metabolites
- Common specimens
- Blood, urine, vitreous humor, tissue
- Screen result status
- Presumptive, not legally definitive on its own
Common questions
Why is a second confirmatory step needed after the screen?+
Immunoassays cross-react with structurally similar compounds and can produce false positives. Chromatography-mass spectrometry identifies a substance by exact mass and fragmentation pattern, which is what makes the result defensible in court.
How is the specimen for a screen chosen?+
Choice depends on the post-mortem interval, the drug class suspected, and what is available. Vitreous humor resists putrefaction and is useful in decomposed cases, while blood remains the standard for quantitation.
Does a negative screen rule out poisoning?+
No. Immunoassay panels only cover a defined set of compounds, so a negative screen rules out those substances, not novel psychoactive substances or poisons outside the panel, which need targeted confirmatory testing.
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