Erythrocyte sedimentation rate

From greek.doctor

Erythrocyte sedimentation rate (ESR), also called the Westergren method (We), is a laboratory measurement of how quickly the erythrocytes in a sample sediment (settle on the bottom of the tube). The ESR increases in response to the acute phase reaction (inflammation), but it takes many days for the ESR to increase following an inflammation, and it takes weeks to normalise. The normal value depends on age and gender but is around < 15-30 mm/h.

It used to be the main parameter to measure when evaluating inflammation and infection, but nowadays other parameters are preferred, like CRP and leukocyte count. However, there are still some scenarios where the ESR is useful to measure.

Indications

Giant cell/temporal arteritis, polymyalgia rheumatica, rheumatoid arthritis, and Hodgkin lymphoma are conditions in which an elevated ESR is more specific and sensitive than an elevated CRP or leukocyte count.

Test procedure

Measurement of erythrocyte sedimentation rate usually requires a venous blood sample in a special black tube used only for ESR. In this tube, 4 parts blood are mixed with 1 part isotonic sodium citrate solution. The tube must then be placed vertically and some time must pass (usually 1 hour), after which the rate at which the erythrocytes have sedimented can be calculated. A regular EDTA-tube may also be used.

Pathophysiology

During inflammation and infection, the acute phase reaction is initiated, which increases the level of immunoglobulins, fibrinogen, and other positively charged acute phase proteins. Albumin is negatively charged, and its level is decreased during the acute phase reaction. As such, the albumin/globulin ratio decreases.

RBCs have negatively charged surfaces, while most plasma proteins are positively charged. Normally, the negative charges on the RBCs repel each other, but when the amount of positively charged plasma proteins increase, these charges are neutralised, making RBCs stick to each other in a characteristic stack similar to a stack of coins called a rouleau. These rouleaux sediment faster than regular RBCs.