The sedimentation rate is the time that red blood cells take to settle at the bottom of a thin, vertical tube. Red blood cells tend to sediment more quickly when the blood contains proteins associated with the inflammatory response, such as C-reactive protein and others. The sedimentation rate is an indirect measure of the degree of acute or chronic inflammation that affects an individual (infections, autoimmune diseases, cancers, etc.).
The faster the sedimentation rate, the more severe the inflammation. The result can not, however, be used to diagnosis a particular disorder. The sedimentation rate can also track the efficacy of anti-inflammatory treatment, but there are other more specific markers, such as C-reactive protein (CRP) levels. Individuals with multiple myeloma, a bone marrow disorder characterized by excess antibody production, typically have very high sedimentation rates with no inflammatory symptoms (normal CRP levels).
A below-normal sedimentation rate may indicate an abnormally high number of red blood cells (polycthemia or polyglobulia) or white blood cells (leukocytosis) or a protein abnormality. Changes in the shape of the red blood cells can also cause sedimentation rates that are low (sickle cell anemia, etc.).