Predictive equation to estimate post-mortem interval using spectrophotometric blood-colour values

Forensic pathologists use post-mortem phenomena to estimate the post-mortem interval (PMI). We have reported on the usefulness of post-mortem lividity spectrophotometric values to estimate PMIs. Here, we focused on blood colour, looking for associations between blood colour, age and PMI. We generated predictive equations for blood-colour values and the PMI. We included data from a total of 129 cadavers (84 males and 45 females). We measured the colour of 124 left ventricular blood ( L*_l, a*_l, b*_l), 123 right ventricular blood ( L*_r, a*_r, b*_r) and 57 femoral blood ( L*_f, a*_f, b*_f) samples. We found no significant associations between blood colour and age or between blood colour and the PMI, but the values of a*_l, b*_l, a*_r and b*_r were significantly increased with increased age, and those of L*_f, a*_f and b*_f were significantly decreased with increased PMI. We created equations to estimate blood colour. The equations for femoral blood colour had higher adjusted R² values and lower root mean square error values than those for left and right ventricular blood colours. We generated equations to estimate PMIs using blood-colour values and autopsy findings. Our estimated PMIs up to 67 hours had accuracies within 8.84 hours, without measuring post-mortem lividity colour or considering the age of the deceased. This is the first study to estimate PMIs based on blood-colour spectrophotometric values.