Postmortem Clinical Chemistries Vitreous Flashcards
Postmortem vitreous chemical analysis
Also called vitreous (bio)chemistry
Common ancillary study
In many cases pivotal for determining cause and manner of death
Why is vitreous Ideal for postmortem chemical analysis
Isolated from blood and other body fluids that are affected by postmortem changes
Redistribution and hemoconcentration
Resists putrefaction longer than other body fluids, although it is not entirely immune to it
Vitreous fluid can be analyzed from bodies that have been previously embalmed
Eye is isolated and well protected anatomically
Vitreous humor is usually well preserved despite serious trauma to the head
Less subject to contamination
Vitrous humor valuable alternative matrix
High H2O content low MW non-protein bound compounds will equilibrate
Vitreous interpretive value in assessment of alcohol
Absorptive/post-absorptive phase
Antemortem consumption vs. neo-formation
Prevent false pos due to specimen mix-up
WHich is more stable PM chemical comp of blood, CSF or vitreous
Vitreous
Vitreous fluid within globe of an eye between retina and lens
Acellular, viscous [2-4 x water], and colorless
Predominantly (99%) water
Glucose [very small amount except in hyperglycemic pts]
Hyaluronic acid
Collagen fibers (type II)
Inorganic salts
Ascorbic acid
Post mortem chemistries may be useful in a variety of situations
Demonstrate biochemical abnormalities reasonable for death
Help in the evaluation of the psychological effects of recognized pathology
(??) assist in estimating the time of death
Three major factors to consider in the evaluation
Sample time
Sample source and acquisition
Analytical methodology
Sample Time
Samples should be obtained during early postmortem interval
Time between death and onset of putrefaction
Characterized by relatively clear/colorless viscous fluid
With the onset of decomposition fluid becomes cloudy and brownish in color
Sample sources and Acquistion
Suction should be applied gently and gradually
Vacuum tubes should be avoided
Initial strong suction causes fragments of the retina or other tissue to contaminate the specimen
How much from each eye
2-3 mL of the vitreous from each eye
1 mL from even infants
What tubes for vitreous
red top or gray top tubes
Vitreous fluid analytes
urea nitrogen, glucose and electrolytes
Individuals dying of unexpected natural disease will yield significant results in over 5% cases
Reflect antemortem serum concentration of Na+, Cl-,and urea
Coe and Apple Study
studied glucose, urea, nitrogen, sodium, potassium, and chloride on a variety of instrumental platforms
Variation in values obtained by different procedures/instruments
Variations did not cause any interpretive problems for glucose and urea nitrogen , however did impact electrolytes
Glucose
Significant increase blood glucose agonal stages of life
Increases reported in asphyxial deaths, cerebral hemorrhage, congestive heart failure and electrocutions
Commonly seen in cases w/ cardiopulmonary resuscitation
May be related to terminal stress w/ secretion of catecholamines, subsequently glycogenolysis
Vitreous glucose >200mg/Dl indicative of
Antemortem hyperglycemia
No reliable method to determine hypoglycemia
