Hyponatremia at autopsy: an analysis of etiologic mechanisms and their possible significance.

While electrolyte measurements after death may be confounded by a number of variables, vitreous humor sodium tends to remain stable for some time, enabling correlation between ante- and postmortem levels. Review of natural and unnatural causes of reduced vitreous humor sodium levels at autopsy was undertaken to demonstrate the range of diseases that may result in this finding. Natural diseases affecting the vasopressin-renin-angiotensin axis may cause reduction in sodium levels with associated hypovolemia, euvolemia, and hypervolemia. Low sodium measurements may also occur with redistribution of water, and artefactually when there are underlying lipid and protein disorders. Unnatural causes of hyponatremia at autopsy include water intoxication from psychogenic polydipsia, environmental polydipsia, ingestion of dilute infant formulas, beer potomania, endurance exercise, fresh water immersion (including water births) and iatrogenic causes including drug and parenteral fluid administration, and surgical irrigation. A knowledge of the range of conditions that may result in lowered postmortem sodium levels will help to exclude or confirm certain diseases at autopsy. In addition, significant vitreous hyponatremia may be a useful finding to help clarify mechanisms of unnatural deaths.