Procedures

This section covers the various aspects of toxicology lab procedures

General Principles of Toxicology Laboratory Test Procedures

Objective: To identify and quantify toxic substances in biological samples for clinical, forensic, and environmental purposes
Scope: Encompasses a wide range of analytes, including drugs, poisons, heavy metals, and environmental toxins
Types of Assays
- Screening Assays: Provide rapid, qualitative detection of substances or classes of substances
- Confirmatory Assays: Provide quantitative identification and confirmation of specific substances
Sample Types
- Blood, urine, gastric contents, tissues, hair, oral fluid, and other specimens

Immunoassays (IAs)
- Principle: Based on antibody-antigen binding
- Types: ELISA, FPIA, CLIA
- Advantages: High throughput, ease of use
- Limitations: Cross-reactivity, limited quantitative accuracy
Chromatography (GC, HPLC)
- Principle: Separates compounds based on physical and chemical properties
- Detectors: UV-Vis, fluorescence, electrochemical, mass spectrometry (MS)
- Advantages: High resolution, quantitative analysis
- Limitations: Requires skilled operators
Mass Spectrometry (MS)
- Principle: Identifies and quantifies compounds based on mass-to-charge ratio
- Techniques: GC-MS, LC-MS/MS
- Advantages: High sensitivity and specificity, can identify unknowns
- Limitations: Requires expensive equipment and highly skilled operators
Atomic Absorption Spectrometry (AAS)
- Principle: Measures light absorption by free atoms
- Application: Heavy metal analysis
- Advantages: High sensitivity for minerals
- Limitations: Requires specialized equipment, matrix effects
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
- Principle: Measures mass-to-charge ratio of ions in plasma
- Application: Trace elements, heavy metals
- Advantages: High sensitivity, multi-element analysis
- Limitations: Requires specialized equipment, matrix effects

Personnel Safety
- Personal Protective Equipment (PPE)
- Chemical Hygiene Plan
- Fume Hood
- Spill Response
Specimen Handling
- Chain of Custody
- Labeling
- Storage
Instrumentation
- Calibration
- Maintenance
- Quality Control
Waste Disposal
- Chemical Waste
- Biohazardous Waste
Documentation
- Procedures, results, QC data, maintenance logs
Security
- Controlled substances stored securely
- Limited access

General Guidelines
- Sample Integrity: Proper containers to prevent contamination
- Volume: Collect adequate volume
- Timeliness: Process promptly
Specific Specimen Types
- Blood: Gray-top for alcohol, avoid hemolysis
- Urine: Random or timed, preservatives if needed
- Gastric Contents: Collect as soon as possible
- Tissues: Collect during autopsy or biopsy
- Hair: Collect close to scalp, wash and segment
- Oral Fluid: Use specialized collection devices

Unexpected Results
- Verify patient ID
- Repeat the test
- Check for interferences
- Review history
- Consider alternative methods
Quality Control (QC) Failures
- Out-of-Range QC
- Calibration Issues
- Reagent Problems
- Instrument Malfunction
- Action: Investigate and correct the source of the error

Endogenous Substances
- Bilirubin
- Lipids
- Proteins
Exogenous Substances
- Medications
- Herbal Supplements
- Food
- Cleaning Agents
Collection/Handling Materials
- Tube Additives
- Contaminated Containers
Specific Interferences
- Cross-Reactivity
- Matrix Effects
- Heterophile Antibodies
Strategies to Address Interferences
- Dilution
- Extraction
- Cleanup Procedures
- Masking Agents
- Alternate Methods
- Interference Checks