Erythrocyte sedimentation rate
Erythrocyte sedimentation rate, otherwise known as a sed rate, is an in vitro test that is used as a marker of inflammation. ESR is the rate in mm/hour at which red blood cells in an anticoagulated standardized tube settle from plasma and other blood components. The standardized tube typically used for this test is a vertical tube called a Westergren tube. These tubes typically contain sodium citrate as an anticoagulant and were developed by Alf Vilhelm Albertsson Westergren.
There are three stages that occur during the hour that it takes to perform an ESR. They include rouleaux formation, sedimentation stage, and packing stage. When a patient is experiencing inflammatory conditions, they have an increased amount of fibrinogen and other clotting proteins in their blood, which causes increased rouleaux formation. Rouleaux is best described as a formation that happens when plasma proteins are high. Red blood cells aggregate together and form stacks, which then begin to settle at the bottom of the Westergren tube and pack together. Under normal conditions, red blood cells are negatively charged and repel each other, so the rouleaux formation does not happen and the sed rate is 0 mm/hr or close to it.
ESR is a nonspecific marker for inflammation. At Solaris Diagnostics, 1.5 mL of EDTA whole blood is aliquoted into a Westergren tube and allowed to settle for one hour. At the end of the hour, there is a definitive line between the packed red cells and the plasma, and the amount of settling is recorded in mm/hr. Abnormal ESR values include anything above 30mm/hr. A patient’s ESR will be increased in instances of rheumatoid arthritis, lupus, anemia, thyroid disease, kidney disease, multiple myeloma, systemic infections, and a host of other conditions and diseases.
