The erythrocyte sedimentation rate or more colloquially sed rate is a measurement of how much of the volume of red blood cells will form sediment at the bottom of a test tube after a period of one hour. It is a common blood test and can be correlated with generalized inflammation.
In normal blood, there are two forces that work in opposition, one that makes blood tend to fall with graviational pull, and another that helps keep it suspended in solution. When inflammation is present, red blood cells tend to stick together, making it far more likely they will fall out of solution over time.
The sed rate is commonly higher in patients who are pregnant, have an inflammatory disease such as arthritis and those with anemia. It is lower in patients with polycythemia, Sickle cell anemia and congestive heart failure.