A new perspective in the estimation of postmortem interval (PMI) based on vitreous [K+]

The relation between the potassium concentration in the vitreous humor, [K], and the postmortem interval has been studied by several authors. Many fo rmulae are available and they are based on a correlation test and linear re gression using the PMI as the independent variable and [K+] as the dependen t variable. The estimation of the confidence interval is based on this form ulation. However, in forensic work, it is necessary to use [K+] as the inde pendent variable to estimate the PMI. Although all authors have obtained the PMI by direct use of, these formulae , it is, nevertheless, an inexact approach, which leads to false estimation s. What is required is to change the variables, obtaining a new equation in which [K+] is considered as the independent variable and the PMI as the de pendent. The regression line obtained from our data is [K+] = 5.35 + 0.22 P MI, by changing the variables we get PMI = 2.58[K+] - 9.30. When only nonho spital deaths are considered, the results are considerably improved. In thi s case, we get [K+] = 5.60 + 0.17 PMI and, consequently, PMI = 3.92[K+] - 1 9.04.