Vitreous humor chemistry: the use of potassium concentration for the prediction of the postmortem interval.

Upon review of the literature, extensive disagreement was found as to the usefulness of vitreous humor potassium concentration as a predictor of the postmortem interval (PMI). A pilot study of 1427 cases was performed to address this problem. The requisite statistical analysis for the prediction of PMI is inverse prediction. The 95% inverse prediction interval was found to be approximately +/- 20 h. The linear regression equation for the data was y = 0.238 chi + 6.342, with a coefficient of determination (r2) of 0.374. This r2 value means that 62.6% of the variation of potassium is unaccounted for by the variation in PMI. Further studies are required to attribute this unaccounted variation to quantifiable factors. This would narrow the inverse prediction interval and enable vitreous potassium to be a useful aid in the prediction of PMI.