Overview The rate at which RBCs fall in a test tube forming a measurable clear supernatant ↑ ESR caused by infections inflammation inflammation results in increased acute phase reactants (e.g. fibrinogen) which results in RBC agglutination agglutination causes RBCs to fall at a faster rate within the test tube e.g. temporal arteritis and SLE cancer pregnancy greater plasma volume results in easier formation of a clear supernatant due to decrease in density of plasma relative to density of a single RBC increase in acute phase proteins (e.g. fibrinogen) promotes RBC aggregation ↓ ESR caused by sickle cell changes in RBC morphology result in altered sedimentation polycythemia more RBCs take longer to create a supernatant CHF