The Erythrocyte Sedimentation Rate (ESR), or 'sed rate' is a crude measure of inflammation. An elevated ESR (ie over 100) suggests inflammatory process- infectious, immunologic or neoplastic (ie multiple myeloma).
The rate at which a RBC falls to the bottom of the test tube. If there is increased immunoglobulins or plasma proteins (paraproteins), then the red blood cells stack together forming rouleaux. These are heavier and fall to the bottom of the tube faster.
A rule (to be used with great caution) to calculate upper limits of normal:
Fibrinogen or antibodies neutralize the negative charges of RBCs, allowing their interaction and accelerated settling.
ESR increases with age, anemia, renal failure and in pregnancy.
ESR decreases with changes in RBC morphology, congestive heart rate and cryoglobulinemia.