SUBJECT AREA · 15 GUIDES
Specimens & Matrices
How collection, preservation, storage, and biological matrix affect what a result can mean.
Specimen Collection in Toxicology
Collection is the first analytical step. Tube type, site, timing, volume, labeling, and handling can affect the integrity and meaning of every later result.
Specimen Adulteration Testing
Adulteration testing looks for substitution, dilution, oxidants, or other manipulation. A validity finding should be tied to the measured marker and applicable criteria.
Urine Specimen Validity Testing
Creatinine, specific gravity, pH, and selected adulterant tests help assess whether urine is consistent with an authentic, usable specimen.
Dried Blood Spot Toxicology
Dried blood spots require little volume and simplify storage, but hematocrit, spot uniformity, extraction, and sampled area may influence results.
Meconium Toxicology
Meconium testing can provide evidence of prenatal exposure across part of pregnancy, but formation timing, deposition, collection, and analyte stability complicate timing claims.
Umbilical Cord Toxicology
Umbilical cord tissue is convenient after delivery and can show prenatal drug exposure. It is not interchangeable with meconium, urine, or maternal blood.
Specimen Storage and Stability
Temperature, light, time, preservatives, container material, and freeze-thaw cycles can change analyte concentration or availability.
Oral Fluid Toxicology
Oral fluid can reflect relatively recent exposure and is useful for observed collection. Drug entry from blood and the mouth creates analyte-specific interpretation issues.
Hair Testing in Toxicology
Hair can extend the detection window for repeated exposure, but cosmetic treatment, external contamination, growth variability, and sampling location constrain interpretation.
Biological Matrices
Blood, plasma, serum, urine, oral fluid, hair, and tissues contain different information. Results should not be translated across matrices without evidence.
Hemolysis and Toxicology
Hemolysis releases cellular material into plasma or serum and can change appearance, matrix composition, or certain measurements.
Small-Volume Toxicology
Small specimens force tradeoffs among screening, confirmation, repeats, and preservation. Methods must be validated for the actual volume used.
Whole Blood vs Plasma
Drug concentrations can differ between whole blood and plasma because compounds partition between cells and fluid. Conversion factors are drug-specific and uncertain.
Serum Toxicology
Serum is collected after blood clots and is common in clinical testing. Forensic comparison requires attention to matrix-specific methods and reference information.
Urine Toxicology Interpretation
Urine testing is sensitive to prior exposure because drugs and metabolites accumulate during excretion. It usually cannot establish present impairment or precise timing.