Estimation of the postmortem interval by analyzing potassium in the vitreous humor: could repetitive sampling enhance accuracy?

The relationship between the postmortem interval and the potassium concentration in the vitreous humor has been described by different authors. A limitation of most previous studies might be that all of the vitreous humor has been extracted in 1 sample from different subjects and that the sample was therefore inhomogeneous. In 32 traumatic deaths with known postmortem intervals, small quantities of vitreous humor have been sampled repetitively in 3-hour interval. The bodies were stored at 20°C. The average concentrations of potassium in relation to the postmortem interval were 6.11 to 14.46 mmol/L. An equation that allows accurate prediction of the postmortem interval was established: postmortem interval (h) = 2.749 × [K] - 11.978.

Could lactates in vitreous humour be used to estimate the time since death?

Vitreous humour (VH) is a useful medium for postmortem analysis. During the supravital period, anaerobic glycolysis that occurs results in the increased lactate concentration (L) in cytosol. We analysed the concentration of lactic acid in 567 samples of VH from 63 autopsy cases by a repetitive withdrawal of VH from the same corpse, while the outside temperature remained constant. The samples were taken from the same eye in intervals of three hours for the period of 24 hours. The subjects were divided into two groups: group 1 included individuals who died during winter and were kept for analysis at 40C, while group 2 consisted of those who died during spring and autumn (continental climate) and were stored at 200C. Only the cases of a sudden traumatic death of previously healthy individuals were included in the study. Statistically significant correlation of L against postmortem interval (PMI) was observed in the group 1 experiment (r = 0.675; P < 0.01), but the effect of hypothermia made the estimation of PMI practically impossible. A much stronger correlation of L against PMI was observed in group 2 (r = 0.866, P < 0.01); a functional relationship between PMI and L were demonstrated using the formula PMI = 1.696 x L - 10.562, which enabled more accurate prediction of the PMI.

The role of vitreous magnesium quantification in estimating the postmortem interval.

The use of magnesium as a parameter to estimate the time of death is controversial. In 32 traumatic deaths with known postmortem intervals (PMIs), small quantities of vitreous humor (VH) were sampled repetitively every 3 h until 24 h postmortem. The bodies were kept at the constant ambient temperature of 20°C (68°F). The concentrations of magnesium were in the range of 0.47-1.15 mM. A statistically significant correlation of the concentration of magnesium with the PMI was observed (r = 0.453, p < 0.01), but with small predictive value--coefficient of variation for regression was 45.5%; the average of the paired differences between the estimated and actual PMIs was 5.24 + 3.19 h. Although useful results might be expected due to the large transmembrane gradient for magnesium, the results of this study strongly disprove the usefulness of measuring magnesium in VH to estimate the time of death.