Erythrocyte sedimentation rate (ESR, Sedimentation Rate, Sed Rate, Westergren Sedimentation Rate)
The erythrocyte sedimentation rate (ESR) is a non-specific measure of inflammation.
To perform the test, some anticoagulant (a substance preventing the coagulation of blood) is added into the blood, and the anticoagulated blood is placed in an upright tube for 1 hour. Since plasma has a lower specific weight than red blood cells, the red blood cells fall because of gravity. The blood separates into two layers. The bottom layer is composed of red blood cells, while the upper layer is plasma. In an hour, the ESR is determined by the height of the column of plasma in millimeters. The erythrocyte sedimentation rate is indicated by the number of scale marks at the border between the two layers and is measured in mm/h.
When inflammation occurs, fibrinogen (one of the proteins of the acute phase of inflammation) and globulin (protective antibodies released into the blood in order to fight inflammatory agents, including bacteria, viruses, fungi, etc.) levels rise in the blood causing the red blood cells to stick to each other and settle to the bottom and increasing the ESR.
Normally, the ESR begins to increase within 24-48 hours after the development of the disease and increases greatly during the second week, occasionally reaching its peak levels during the recovery period. This can be explained by the fact that the body needs some time to produce enough antibodies. Repeated ESR tests performed over time are more informative rather than a single ESR test.
The ESR is impacted by multiple factors. During pregnancy, changes in protein composition of the blood occur increasing the ESR.
The ESR may fluctuate throughout the day reaching its peak levels during the daytime.
The ESR may increase in acute infectious and inflammatory processes in 24 hours after the increase in body temperature and number of white blood cells.
An increased erythrocyte sedimentation rate may occur in chronic inflammation due to the increase in fibrinogen and immunoglobulin concentrations.
The ESR is also impacted by blood viscosity and total red blood cell counts. For example, an increased ESR may occur in anemia which reduces blood viscosity, while a low ESR may occur in erythrocytosis (an increase in red blood cell) due to an increased blood viscosity.