Podcast
Questions and Answers
Immunoassays are only used for confirmation of drug presence.
Immunoassays are only used for confirmation of drug presence.
False
Gas chromatography and mass spectrometry (GC/MS) are considered a gold standard in toxicological analysis.
Gas chromatography and mass spectrometry (GC/MS) are considered a gold standard in toxicological analysis.
True
In clinical toxicology, patient consent is required for testing.
In clinical toxicology, patient consent is required for testing.
False
False positive results in immunoassays can occur due to cross-reactivity with other substances.
False positive results in immunoassays can occur due to cross-reactivity with other substances.
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A screening result is sufficient for legal action in forensic toxicology.
A screening result is sufficient for legal action in forensic toxicology.
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Liquid chromatography is a type of analytical chromatography used in toxicology.
Liquid chromatography is a type of analytical chromatography used in toxicology.
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Both therapeutic drug monitoring and workplace drug testing are considered aspects of forensic toxicology.
Both therapeutic drug monitoring and workplace drug testing are considered aspects of forensic toxicology.
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Codeine can give a positive reaction for morphine in immunoassays.
Codeine can give a positive reaction for morphine in immunoassays.
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Gas Chromatography involves a process that is non-destructive to the chemical being analyzed.
Gas Chromatography involves a process that is non-destructive to the chemical being analyzed.
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High Performance Liquid Chromatography is preferred for substances that are heat-labile.
High Performance Liquid Chromatography is preferred for substances that are heat-labile.
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Gas Chromatography is slower than High Performance Liquid Chromatography.
Gas Chromatography is slower than High Performance Liquid Chromatography.
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Mass Spectrometry sorts ions based on their mass-to-charge ratio.
Mass Spectrometry sorts ions based on their mass-to-charge ratio.
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False positives occur when a drug is detected in a sample but is not actually present.
False positives occur when a drug is detected in a sample but is not actually present.
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The term 'gold standard' refers to the combination of Gas Chromatography and Nuclear Magnetic Resonance.
The term 'gold standard' refers to the combination of Gas Chromatography and Nuclear Magnetic Resonance.
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Dilution can lead to false negatives in drug testing results.
Dilution can lead to false negatives in drug testing results.
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HPLC is the method of choice for analyzing volatile substances.
HPLC is the method of choice for analyzing volatile substances.
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Study Notes
Toxicological Aspects of Substance Abuse
- Toxicology is the study of harmful effects of toxins.
- Toxicology can be clinical or forensic.
- Clinical toxicology focuses on emergency screening (e.g., overdose), toxic exposure, and therapeutic drug monitoring (TDM) for medical evaluation.
- Forensic toxicology focuses on postmortem examinations, criminal cases, workplace drug testing, and sports.
Clinical vs. Forensic Toxicology
| Feature | Clinical | Forensic |
|---|---|---|
| Patient consent | Not required | Required |
| Specimen identity | Presumed | Proved |
| Screening results | Sufficient for medical decisions | Only confirmed results are considered positive |
| Results use | Medical evaluation | Legal action |
Analytical Problems in Toxicology
- Endogenous substances (e.g., cholesterol, fats, proteins, putrefactive amines) can present analytical challenges.
- Drugs have a vast range of therapeutic concentrations (over 100,000-fold).
- Some drugs can vary in concentration by over 1000-fold.
- Detecting some drugs might be difficult due to concentrations or analytical conditions not being appropriate.
- Some drugs or poisons may be very unusual.
Analytical Basis of Toxicology
- Immunoassay
- Used for preliminary screening.
- Measures the reaction between antibodies and antigens (drugs/metabolites).
- Can detect small amounts of drugs/metabolites, but may suffer from cross-reactivity.
- ELISA and RIA are example immunoassays.
- Chromatography (TLC, GC, HPLC)
- Separates mixtures based on affinity between a mobile and stationary phase to identify and quantify substances.
- Often used after preliminary immunoassay.
- GC/MS (Gas chromatography-mass spectrometry) is a gold standard technique for analysis.
Disadvantages of Immunoassay
- Specificity issues can lead to false positives with other compounds/drugs.
- Cannabinoids, NSAIDs (e.g., ibuprofen, naproxen), and codeine could produce false positives in immunoassay.
- Anti-histamines can induce false positive responses to amphetamines.
- Immunoassays are good for screening, but not always accurate for confirmation.
Chromatography (GC, HPLC)
- Chromatography aims to separate a mixture.
- Samples have differing affinities between the mobile and stationary phases to generate separation for identification.
- Gas Chromatography (GC) often followed by Mass Spectrometry (MS); useful for volatile substances.
- High-Performance Liquid Chromatography (HPLC) uses liquids and is better for compounds that are difficult to volatilize (e.g., steroids).
Mass Spectrometry
- Ionizes chemical samples; sorts the ions by mass-to-charge ratio for analysis.
- Useful in conjunction with chromatography for identification.
- Generates mass spectra for identification.
Interpretation of Test Results
- False negatives: Drug present but not detected (threshold too high, too low quantities).
- False positives: Drug detected but not present (interfering substances, cross-reaction with reagents, or illicit adulterations).
Mission of National Poison Centre (Example)
-
Reduce mortality, morbidity, costs and occurrence of poisoning.
-
Via services, the centre reduces risk of poisoning:
- Provides information on poisons, advice on managing cases.
- Conducts research and documents poisoning incidences.
- Coordinates and conducts poison awareness and prevention education.
- Carries out analytical tests and interprets lab results.
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Description
Test your knowledge on the principles of toxicology, including immunoassays, chromatography techniques, and the role of patient consent. This quiz covers essential topics in forensic toxicology, analytical methods, and implications for drug testing. Prepare for questions related to false positives and the use of gas chromatography and mass spectrometry.
