Estimation of Postmortem Interval Based on the Third Component of Complement (C3) Cleavage

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To estimate postmortem interval(PMI), spontaneous cleavage of the third component of complement (C3) was studied in aged blood and cadaveric blood by crossed immunoelectrophoresis. C3 cleavages in vitro at different temperatures showed that the incubation of whole blood at a higher temperature led to a faster conversion of beta IC (native C3) to beta 1A (C3_c). In cadaveric blood, we found a significant positive correlation between percentage of C3 cleavage and pmi. From these results, it is possible to estimate PMI from the ratios of C3 cleavege. Using the kinetics of C3 cleavage in vitro described as dC/dt = -kC, where C is the consentration of native C3 at time t and k is a first-order rate constant, Arrhenius' equation, and another equation which assumes a linear drop of body temperature after death, the percentages of C3 cleavage were calculated. There was a significant positive correlation between the calculated percentages and the measured percentages of up to 10% in cadaveric blood. We found that the comparison between the calculated percentage of C3 cleavage for each optional postmortem interval and the measured percentage of up to 10% in cadaveric blood leads to the estimation of PMI. This approach is one step towards the development of an accurate method for determining PMI based on C3 cleavage, that is, on a first-order reaction.