Autopsy & forensics
General
Postmortem chemistry
Author: Sarah Avedschmidt, M.D.
Last author update: 1 March 2016
Last staff update: 26 August 2019
Copyright: (c) 2002-2019, PathologyOutlines.com, Inc.
PubMed Search: Postmortem chemistry [title]
Cite this page: Avedschmidt S, Brown TT. Postmortem chemistry. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/forensicschemistry.html. Accessed June 10th, 2023.
Definition / general
- Biochemical analysis of body fluids (blood, urine, cerebrospinal fluid and vitreous humor) to measure endogenous constituents in dead bodies helps determine the cause of death
- Postmortem chemistry has become an important ancillary procedure for the forensic pathologist (Am J Forensic Med Pathol 1993;14:91)
- Specimens must be collected, labeled, stored and analyzed under established, standardized conditions (Connolly: Autopsy Pathology: A Manual and Atlas, 3rd Edition, 2015)
Sites
Blood
Vitreous Humor
Synovial Fluid
Urine
Cerebrospinal Fluid
Bile
Gastric Contents
Hair
Fingernails
Fibroblasts for Tissue Culture
Tissue
- Peripheral venous / arterial specimens best approximate antemortem values
- For toxicology, recommended to use femoral or subclavian vessels, via percutaneous collection with large bore needle and syringe
- 40 - 50 mL required
- Place portion in fluoride preservative and portion in anticoagulant
Vitreous Humor
- Most frequently used specimen for postmortem analysis
- Isolated and protected by the orbit, less subject to putrefaction than blood
- Not subject to diffusion of drugs and alcohols from the stomach
- Also free of erythrocytes
- Collect with small syringe attached to an 18 gauge needle, using gentle suction to remove all vitreous (2 - 5 mL in adult, 1 mL in newborn)
- Fluid from each eye is stored separately
Synovial Fluid
- Rarely used as substitute for vitreous humor
- About 1 mL can be aspirated from each knee joint
Urine
- Collect with large bore needle attached to syringe once bladder is exposed at autopsy or by urethral catherization before autopsy
Cerebrospinal Fluid
- Aspirated from cisterna magnum with needle, by standard percutaneous posterior lumbar puncture
- Aspirate through the spinal foramina after organ evisceration or by inserting a needle into a lateral ventricle after removing the skull cap, reflecting the dura and separating the cerebral hemispheres
Bile
- Rarely used
- Aspirate from gallbladder or directly from common bile duct in patients status post cholecystectomy
Gastric Contents
- Rinse external stomach with water
- Puncture stomach wall and pour stomach contents into bag
Hair
- Hair should be obtained by pulling to include hair roots
- Adequate sample is 0.5 g for DNA analysis, up to 10 g for analysis of heavy metals
- Tie together while maintaining orientation of hair roots
Fingernails
- Acquired by clipping or removing the entire nail
Fibroblasts for Tissue Culture
- Can be used for karyotyping, metabolic assays, enzyme assays and diagnostic ultrastructural studies
- Collect from skin, fascia, lung, diaphragm, muscle and cartilage
- Samples are placed in sterile tube containing culture medium (RPMI or MEM)
Tissue
- Liver, brain, kidney, cardiac muscle, skeletal muscle and peripheral nerve can be used for metabolic studies and nucleic acid analysis
- Should be obtained shortly after death and frozen rapidly in liquid nitrogen or dry ice and stored at -70°C
Laboratory
Postmortem Chemical Changes in Pathological Conditions
-
Diabetic ketoacidosis
- Vitreous glucose concentration (> 200 mg/dL or > 11.1 mmol/L) is the most reliable marker
- Also reliable are ketone bodies, urine glucose and glycated hemoglobin
- Increased postmortem serum and vitreous urea nitrogen levels (> 40 mg/dL)
- Increased vitreous sodium (> 155 mEq/L) and chloride levels (> 135 mEq/L)
- Normal postmortem serum and vitreous creatinine levels
- Pituitary, adrenal cortical and a few other hormone concentrations will reflect antemortem levels
- Epinephrine and insulin levels are unstable postmortem
- Mast cell granules contain proteases such as tryptase and chymase which are degranulated during anaphylactic reactions
- Hypothermia results in an increase in ketone bodies in the blood and urine
- Alcohol consumption inhibits ketogenesis
- There is an inverse statistically significant relationship between ketone body blood levels and ethanol levels (Connolly: Autopsy Pathology: A Manual and Atlas, 3rd Edition, 2015)
- Serum procalcitonin increases (> 100 ng/ml) in severe systemic bacterial infections
- Acute phase proteins and cytokines can be used in postmortem chemistry similarly to clinical practice
- Serum and urine neopterin is increased in cases of fatal bacterial and viral infections
- Hypoglycemia cannot be reliably tested
- Ratio of insulin to C peptide can be used
- Aminotransferases are not reliable postmortem
- Albumin-globulin ratio is reliable
- Decreased sodium and chloride concentrations
- Increased potassium concentrations (> 20 mEq/L)
- Increased thyroglobulin and T3 concentrations in postmortem serum from heart blood
Dehydration
Endocrine Disorders
Anaphylaxis
Hypothermia
Sepsis
Insulin Overdose
Liver Disease
Decomposition
Incomplete suspension / manual strangulation
Interpretation
- Alcohol misuse: carbohydrate deficient transferrin, ethyl glucuronide, ethyl sulphate
- Anaphylaxis: tryptase, chymase
- Cardiac function: atrial natriuretic peptide, brain natriuretic peptide, myocardial ischemia (troponin I, troponin T, myosin, myoglobin, creatine kinase and creatine kinase MB)
- Electrolytes: sodium, chloride, calcium, magnesium, strontium
- Glucose metabolism: glucose, glycated hemoglobin, ketone bodies, insulin, peptide C
- Liver function: total cholesterol, total bilirubin, total protein
- Renal function: urea nitrogen, creatinine, uric acid
- Sepsis/Inflammation/Infection: procalcitonin, acute phase proteins and cytokines, neopterin
- Hormones: adrenocorticotropic hormone; thyroid stimulating hormone / thyroglobulin / thyroid hormones; catecholamines; cortisol; chorionic gonadotropin; erythropoietin ; chromogranin A; S100B; serotonin, myoglobin
Additional references
