In vitro loss of potassium from erythrocytes during the 0-108 h postmortem period in rats: relationship between potassium loss and postmortem interval.

A simple technique was employed for measurement of potassium loss (K(los)s) from normal and from postmortem rat erythrocytes during controlled exposure to physiologically isosmotic NaCl solution. Potassium loss from the cells decreased in a (non-linear) time-related manner during the 0-108 h postmortem period; expression of the data in the form of a double logarithmic plot (log K(loss) versus log postmortem interval (PMI) linearized the relationship between 18 and 108 h post mortem (r = -0.86; P less than 0.001 (n = 24)). Experimental data revealed that the observed postmortem changes in K(loss) were associated with and probably resulted from, the postmortem decrease in magnitude of the potassium concentration gradient across the erythrocyte membrane. Attention is drawn to the possibility of utilizing measurements of in vitro loss of potassium from erythrocytes as a means of estimating time elapsed since death.