Vitreous Sodium
Definition
The sodium concentration in the vitreous humour of the eye; reduced below normal in freshwater drowning (systemic haemodilution) and elevated in saltwater drowning. A stable post-mortem biochemical marker for electrolyte shifts that occurred ante-mortem.
- Body fluid
- Vitreous humour of the eye
- Freshwater drowning
- Sodium reduced (haemodilution)
- Saltwater drowning
- Sodium elevated
- Stability
- Resists post-mortem change longer than blood electrolytes
Common questions
Why does drowning medium change vitreous sodium in opposite directions?+
In freshwater drowning, hypotonic water is absorbed across the lungs into the bloodstream, diluting sodium. In saltwater drowning, hypertonic water draws fluid out of the circulation, concentrating sodium. Both shifts occur while the heart is still beating, so they reflect ante-mortem physiology rather than an artefact of death.
Does a normal vitreous sodium level rule out drowning?+
Not by itself. Sodium shifts depend on how much water was aspirated and how long the person survived after aspiration, so a normal result does not exclude drowning; pathologists interpret it together with diatom testing and scene findings.
Related terms
- Diatom Test
- A laboratory test for ante-mortem submersion in which bone marrow (from sealed femur diaphysis) is acid-digested and the diatom species identified in...
- Dry Drowning
- Drowning in which laryngospasm seals the glottis, preventing water entry into the lungs. The victim asphyxiates without pulmonary aspiration. Autopsy shows non-specific...
- Frustule
- The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- Pollard 1998 Protocol
- The standardised diatom test protocol published in Forensic Science International by A.M. Pollard (1998), specifying acid digestion conditions, wash steps, microscopy method,...
- Secondary Drowning
- Death from delayed non-cardiogenic pulmonary oedema occurring hours to days after an immersion and aspiration event, even if the victim was apparently...
- Washerwoman Hands
- White, wrinkled, macerated skin on the hands and feet from prolonged water immersion. Indicates duration of immersion, not ante-mortem versus post-mortem submersion.
- Wet Drowning
- Drowning in which water is aspirated into the airways and lungs during the immersion event. Produces over-distended pale lungs, frothy exudate, and...