The physics of how blood settles has to do with the zeta potential between the red cells. The zeta potential is the normal, negative force that exists between red cells and pushes them apart from each other. Things that disrupt the zeta potential make it easier for the red cells to come close to each other, and therefore the cells settle faster in the tube (and the ESR goes up). Things that increase the zeta potential between the red cells (making them more repellant than usual) will cause the red cells to settle at a slower rate, and the ESR will therefore go down.
How does the ESR work?
Source: Pathology Student
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