Biological, Non-Biological and Viscera Matrices in Toxicology

Biological specimens include fluids, tissues and keratinous material. Whole blood, serum, plasma, urine, oral fluid, vitreous, liver, hair and nails have different physiological origins and analytical properties. The distinction between antemortem and post-mortem collection is separate from the matrix name.

Viscera include internal organs such as liver, kidney, stomach and lung. Gastric contents should be distinguished from the stomach wall, even when a local submission protocol groups them. A composite containing several tissues must be reported as a composite rather than as a series of independent organ results.

Non-biological exhibits may include tablets, food, drink, water, environmental samples, containers or residues. They can help investigate a possible source, product identity or contamination pathway. Their analysis is not a direct substitute for evidence of exposure in a person.

Every result must retain its source. A bottle containing liver does not become a blood specimen because a blood-calibrated instrument can produce a peak from its extract. The laboratory needs a method suitable for that material and a conclusion appropriate to its evidential role.

Whole blood contains cells and plasma, whereas serum and plasma are different preparations of the fluid component. Cell partitioning, protein binding and preparation affect measured concentrations. Report the actual material, analyte form and units; a plasma reference range cannot simply be applied to post-mortem whole blood.

Urine can contain parent substances and metabolites after they have been cleared from blood. This may extend detection for selected targets, but concentration depends on hydration, renal handling, collection history and the assay. A positive urine result generally does not establish impairment at a specific earlier event.

Oral fluid can be useful in defined testing programmes. Collection devices, fluid volume, recovery and recent oral contamination affect interpretation. A roadside screening result and a laboratory-confirmed result answer different questions, and neither creates a universal oral-fluid-to-blood conversion.

Hair incorporates substances through several pathways and can also be contaminated externally. Approximate scalp growth informs retrospective assessment, but segments are not exact calendar months. Cosmetic treatment, growth variability, sample alignment and the method affect the result. No universal wash sequence proves that all external contamination has been removed.

Nail clippings can integrate exposure over a different and variable period. Their growth, clipping location and contamination history complicate timing. A positive hair or nail result is not a measured blood concentration from the period in which the material formed.

Vitreous can provide supplementary alcohol or selected biochemical information in a post-mortem investigation. Its relative isolation may help interpretation, but it does not make every result immune to decomposition, timing or analytical problems. Paired blood and vitreous results require an integrated assessment rather than a fixed ratio rule.

Bile and cerebrospinal fluid may provide additional evidence for selected targets when suitable methods exist. Their concentrations cannot be translated into blood concentrations by one class-wide multiplier. Meconium and umbilical-cord tissue address selected prenatal exposure questions, with collection and interpretation specific to that setting.

Gastric contents may contain unabsorbed drugs, food or plant material. Their presence can support an ingestion hypothesis, but residue amount is not the administered dose. An empty stomach does not exclude earlier ingestion, and appearance or odour does not identify the agent.

Liver can be a useful supplementary tissue because it participates in distribution and metabolism. Kidney, brain, lung, muscle or other tissues may be selected for particular questions or when preferred specimens are unavailable. Their utility depends on the target and the laboratory's validated scope, rather than a universal organ-for-poison list.

A tissue measurement is expressed for a defined preparation, often by mass. Homogenisation, extraction and whether free or total analyte is measured matter. Document dilution, units and preparation so a reader can identify what the numerical result actually represents.

Post-mortem concentrations can change through redistribution, degradation, contamination and other processes. Peripheral blood is often useful but not unchanged antemortem blood. A liver result and a central-blood result cannot be combined into a precise reconstruction of the concentration at death without adequate supporting evidence.

Arsenic illustrates the importance of target definition. Total arsenic and individual arsenic species answer different questions. Urinary total arsenic can be influenced by seafood-derived organic forms; a high total result alone does not establish toxic inorganic exposure. Hair and nails have additional contamination and reference-range limitations.

Preserve anatomical information and choose preparation before consuming the sample. A hot digestion intended for total elemental analysis may destroy chemical-species information. A tissue extraction intended for a routine drug panel cannot be assumed to address metals, gases or every plant toxin.

Start by stating the question and the relevant time. Was there exposure, could it relate to observed effects, is a longer-term pattern being investigated, or might a scene item be a source? The answer determines which result would be useful and which inferences would remain unsupported.

In a time-sensitive human-performance or drug-facilitated-crime investigation, prompt appropriate blood and urine collection may improve the chance of detection. Care, consent and lawful collection remain essential. A late specimen is not worthless, but a negative result after delay does not exclude every earlier exposure.

Do not select an unsuitable specimen merely because it is the only one familiar to the team. Contact the laboratory about alternatives and the effect of missing material. If the question cannot be answered from available specimens, state that clearly rather than promising that greater instrument sensitivity will solve it.

A detection window is the period during which a specified analyte can be detected under specified conditions. It is not a fixed property of a drug class. Dose pattern, individual disposition, metabolite selection, collection, storage and the method's reporting threshold can all change it.

Avoid universal tables assigning all opioids, benzodiazepines or pesticides one blood or urine window. Parent drugs and metabolites can persist differently. A sensitive targeted method may detect a substance below a programme's decision cutoff; detectable and reported positive are therefore not always equivalent.

Matrix effects are analytical effects of other sample components on measurement. In LC-MS, co-extracted substances can suppress or enhance ionisation, changing the response without a corresponding change in analyte amount. Extraction recovery is a related but distinct issue: how much analyte survives preparation is not the same as how strongly it ionises.

Validation should examine relevant specimen variability and interference. Appropriate internal standards, sample cleanup and calibration strategies can help control effects, but an internal standard is not an automatic guarantee that every altered or decomposed specimen is quantified correctly. Unexpected responses require investigation under the method's criteria.

For example, a blood-calibrated method may respond differently to a decomposed liver extract. The presence of a peak alone does not establish reliable quantification. The laboratory must show suitability for that matrix or limit the conclusion to what the method supports.

Post-mortem redistribution is a separate biological and physicochemical complication. Central and peripheral results can differ without yielding a universal correction factor. Keep the analytical validity of the measurement separate from whether it can represent a concentration during life.

A relevant scene exhibit can strengthen an exposure hypothesis by providing a possible source for further testing. A medicine in blood and the same medicine in a recovered packet are compatible findings, but that compound may also have other available sources. The relationship needs more than a shared name.

Compare identity, formulation and relevant composition using suitable methods. Concentrations in food and blood are not expected to match numerically: serving size, absorption, distribution and time make them different systems. Equal concentrations are not a requirement for an exposure link, and a different concentration does not by itself exclude one.

Sampling representativeness matters. Contamination may be uneven within a meal, container or powder. A negative tested aliquot does not automatically exclude the target from every part of the original item. Record the sampling method and whether material was mixed or selected before analysis.

Scene and biological specimens need separate custody and contamination controls. Material transferred between them during collection can create misleading agreement. Independent identification and a documented collection process help assess whether the apparent corroboration is informative.

A combined report should state each finding, its source and its limits, then explain how the findings relate. It should not announce deliberate adulteration, a particular offender or homicide solely because a plant alkaloid appears in food and blood. Those questions require the wider investigation.

Post-mortem collection is developed in Post-Mortem Examination and Viscera Collection in Poisoning.

Hair-specific methods and limits are developed in Hair Analysis for Drugs and Chronic Poisoning.

Disposition and metabolites are developed in Drug Metabolism, Distribution and Metabolite Identification.