Postmortem analyses of vitreous fluid

Sammanfattning: The identification of various various medical conditions postmortem is often difficult. Results from analysis of postmortem blood and urine samples are not as appropriate as in living subjects, due to bacterial contamination and postmortem cell degradation. Therefore, vitreous humour – the fluid in the eyeball – has been of substantial value in forensic pathology. Vitreous fluid is easily collected, isolated, and almost bacteria- and cell free, and shows relatively stable conditions after death, making it a better matrix for postmortem biochemical analyses than e.g. blood and serum. Although postmortem analyses of vitreous fluid have been studied quite extensviely, there are still many unanswered questions. Vitreous fluid from over 3,000 deceased subjects were consecutivley collected and analysed for glucose, lactate, pH, electrolytes and gas pressures. Paper I focuses on the postmortem diagnosis of hyperglycemia. We show that vitreous glucose levels decrease the first 12-24 hours after death and are relatively stable after that. We also suggest that lactate should not be used to diagnose antemortem hyperglycemia, due to massive lactate increase from other sources – instead, glucose alone should be used. A vitreous glucose level of 10 mmol/L indicates severe antemortem hyperglycemia. In paper II, we studied the postmortem increase in vitreous potassium levels, which can be used to estimate the time of death. Our results show that postmortem potassium levels are affected by the surrounding temperature and the age of the deceased. We have developed a new equation for the estimation of the time of death that includes potassium, surrounding temperature and decedent age. To facilitate the calculation for the user, we have developed a web application. Paper III deals with the interpretation of postmortem vitreous sodium and chloride levels. We show that vitreous sodium and chloride levels slowly decrease with time of death. Postmortem vitreous sodium and chloride levels correlate well with antemortem serum sodium and chloride levels if corrected for time since death, and may be used to diagnose various antemortem sodium/chloride imbalances, such as dehydration or water intoxication. Sodium imbalances in cases of drownings are most likely due to postmortem diffusion between water and vitreous, rather than the drowning process.

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