What is the time frame for coagulation of blood cells & the resulting separation of the cells and platelets from the plasma in a dead body?

Question

I have had this subject come up repeatedly in the context of a discussion about death and how it affects the body.

I found this statement, which is typical of the common understanding among non-professionals:

"Blood starts to coagulate within minutes of death and pool into layers (e.g., red blood cells at the bottom, platelets and white cells in the middle, and plasma on the top, much like sand sitting still in a glass of water). The blood pools at the lowest part of the body (e.g., the left side of the body if the body is lying on its left side)." ~Cited by a seemingly intelligent non-expert who identifies as a "Blood Drive Coordinator, Blood Donor"

I was corrected by an authoritative person years ago, who claimed that this doesn't actually happen for hours in the body. But now I am doubting their credibility. And I am growing embarrassed of having passed-on this commentary.

I would appreciate knowing if it is possible for this to happen within an hour or so of a person's demise? It appears that there are scant clear answers to this question. I have used a variety of search terms on multiple search engines and research sites.

Thanks.

Answer 1

I am not an expert on this at all, however I did a quick google search using the terms "timeline forensics death" and one of the top hits was a scientific book on the National Centre for Biotechnology Information bookshelf with the title "Methods Of Estimation Of Time Since Death"

This is a fairly short book and broken up into short sections. One of the sections is "Livor mortis" (best I can translate as "colour after death"). This section states:

The final change in the classical triad is livor mortis, which is the purplish-blue discoloration of the skin in the dependent parts of the body due to the collection of blood in skin vessels caused by gravitational pull. Hypostasis develops as spots of discoloration within half an hour to 2 hours. These spots then coalesce to form larger patches, which further combine to form a uniform discoloration of the body's dependant parts that have not been subject to pressure, which appears from 6 to 12 hours. The discoloration becomes ‘fixed’ after a certain period, owing to the disintegration of blood cells and the seepage of hemoglobin. This fixation is confirmed by applying pressure with thumbs and is traditionally used to denote a PMI greater than 12 hours.[12] This method of estimation of PMI required an objective and modern approach, leading to the development of colorimetric methods to estimate PMI from livor mortis.[13]

So it takes between 30 min and 2 hours for discolouration to show, but for this to cover and stabilize takes >6h.