# Toxicological Specimen Collection > Toxicological specimen collection in MBBS Forensic Medicine: blood, urine, viscera, vitreous and hair with correct preservatives and volumes. - Canonical URL: https://prepelephant.com/topics/mbbs/forensic-medicine/toxicological-specimen-collection - Exam / course: MBBS · Subject: Forensic Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Toxicological Specimen Collection", PrepElephant, https://prepelephant.com/topics/mbbs/forensic-medicine/toxicological-specimen-collection ## Direct answer A poisoning conviction lives or dies on the specimens: the right sample, in the right container, with the right preservative, sealed and handed over with an unbroken chain. The classical viscera set is stomach with contents, a loop of small intestine, half the liver and one kidney, plus blood, urine and vitreous humour — preserved in saturated common salt solution for chemical analysis, never rectified spirit when alcohol is in question. Blood for alcohol goes into fluoride-oxalate; vitreous resists putrefaction longest and is the prize specimen in decomposed bodies; hair and nails trap arsenic and other metals for months. In living patients, samples drawn early often outlive the police case — label everything with the time. ## What you must remember - **Viscera set (fatal):** stomach with contents, about 30 cm of small intestine with contents, half the liver (roughly 500 g), one kidney, and in special contexts spleen, brain or lung — each in a separate, labelled, wide-mouthed container. - **Preservative rules:** saturated sodium chloride solution for viscera sent for chemical analysis; sodium fluoride (with potassium oxalate as anticoagulant) for blood meant for alcohol and volatile estimation; no preservative for urine and gastric aspirate if refrigerated; 10% formalin only for histopathology — never for chemical analysis. - **Blood volumes and sites:** about 10-20 mL — peripheral (femoral) blood is preferred in the living; at autopsy, heart blood suffers post-mortem redistribution, so femoral or subclavian samples are better. - **Vitreous humour:** about 2 mL from each eye with a fine needle, self-sealing and putrefaction-resistant — the specimen of choice for alcohol, electrolytes, glucose and urea in decomposed bodies. - **Hair and nails:** full-length hair pulled with roots and unclipped nails for chronic metal poisoning — arsenic and thallium deposit in keratin over weeks, and segmental analysis times the exposure. - **Antemortem collection:** 5-10 mL blood in fluoride tube, 20-50 mL urine refrigerated, vomitus and lavage fluid kept — treatment first, but samples drawn before the poison clears. - **Chain of custody:** containers sealed with the doctor's signature across the seal, labelled with name, date, time, site and preservative, and handed to a named police officer with acknowledgement. - **Special analyses:** carbon monoxide demands blood filled to the brim to exclude air; cyanide needs rapid analysis; organophosphates degrade fast — refrigeration and early dispatch decide the outcome. ## Packaging a suspected fatal poisoning properly A young woman dies after three days of unexplained vomiting; the history whispers arsenic. At autopsy the collection is disciplined. The stomach is ligated at both ends before removal, opened along the greater curvature, contents measured and described, and a portion kept with a strip of gastric mucosa. Half the liver and one kidney go into separate jars under saturated salt solution — enough to submerge the tissue. Femoral blood goes into a fluoride tube; urine is aspirated from the bladder; vitreous is drawn from both eyes in case putrefaction advances before the laboratory opens the parcel. Because arsenic is the working diagnosis, the pathologist also pulls hair with roots and clips all ten fingernails into a dry envelope — the specimens that will still testify when the viscera have degraded. The requisition lists the case, suspected poison and analyses requested; seals are signed across, the parcel handed to the constable against signature. Months later the report returns arsenic in liver, kidney, hair and nails — and the hair segments date the dosing. ## Where the exam and the laboratory meet The classic viva sequence: which preservative for viscera? Saturated salt solution — candidates lose marks writing "rectified spirit", which destroys alcohol estimation. Second: why vitreous humour? Its low bacterial content and protected site make it the last fluid to putrefy — 2 mL, one needle per eye, gentle aspiration. Third: why peripheral over heart blood at autopsy? Post-mortem redistribution moves drugs from solid organs into cardiac blood, spuriously raising levels. Fourth, the living-patient trap: the house officer discards the first lavage return — the best sample the prosecution would have had; every suspected poisoning is a potential court case from the first minute. Finally, gastric contents identify what was swallowed, while blood quantifies what was absorbed — different questions in court. ## Frequently asked questions ### Which preservative is used for viscera sent for chemical analysis? Saturated sodium chloride solution, while blood for alcohol estimation requires sodium fluoride with potassium oxalate — rectified spirit is unsuitable. ### Why is vitreous humour valuable in decomposed bodies? Its sterile, protected environment resists putrefaction longest, yielding reliable alcohol, glucose, urea and electrolyte values when blood and urine have spoiled. ### Which specimens detect chronic arsenic poisoning? Hair pulled with roots and full nail clippings, because arsenic deposits in keratin and persists for months, permitting segmental timing of exposure. ### Why is peripheral blood preferred over heart blood at autopsy? Post-mortem redistribution raises cardiac drug levels as substances diffuse from organs, making femoral blood more representative. ### What is the chain of custody for toxicological samples? Containers are labelled, sealed with a signature across the seal, documented on the requisition and handed to a named police officer with acknowledgement at every transfer.