Erythrocyte Sedimentation Rate (ESR)

The erythrocyte sedimentation rate measures how quickly red blood cells settle in a vertical column of anticoagulated blood over one hour. It is an indirect, long-established marker of inflammation, reflecting changes in plasma proteins — chiefly fibrinogen — that promote red-cell aggregation and faster sedimentation.

Definition

The erythrocyte sedimentation rate is the distance, in millimetres per hour, that erythrocytes fall through plasma in a standardized vertical tube; it rises when acute-phase proteins increase red-cell aggregation, serving as an indirect marker of inflammation.

Scope

This entry explains what the ESR measures, the physical and protein basis of the test, its slow kinetics relative to CRP, the factors that influence it, and its general role as a non-specific inflammatory marker. It is a reference description of the test, not a source of reference ranges, diagnostic cut-offs, or clinical decision rules.

Core questions

• What physically determines how fast erythrocytes sediment?
• Which plasma proteins most influence the ESR?
• Why does the ESR change more slowly than CRP?
• What non-inflammatory factors can alter the ESR?

Key concepts

• Red-cell aggregation and rouleaux formation
• Fibrinogen as the dominant driver
• Westergren method
• Indirect marker of the acute phase response
• Slow kinetics relative to CRP
• Influence of anaemia, age, sex, and immunoglobulins

Mechanisms

Erythrocytes normally repel one another and sediment slowly. During inflammation, increased plasma concentrations of asymmetric proteins, above all fibrinogen, reduce this repulsion and promote rouleaux (stacked red-cell aggregates), which settle faster because they have a higher mass-to-surface ratio. The ESR therefore reflects the plasma protein milieu rather than any single analyte directly. Because fibrinogen and immunoglobulin levels change comparatively slowly, the ESR rises and falls over days, lagging behind the rapid kinetics of CRP. Anaemia, red-cell shape, paraproteins, age, sex, and pregnancy can shift the result independently of inflammation.

Clinical relevance

The ESR is a simple, inexpensive, and historically important marker used to detect and follow inflammation, often interpreted together with faster-responding markers such as CRP. Its slow kinetics and sensitivity to non-inflammatory factors mean it is non-specific. This entry describes the test conceptually and does not provide reference intervals or diagnostic and treatment guidance.

Epidemiology

The ESR remains one of the most widely performed laboratory tests for inflammation worldwide owing to its simplicity and low cost, and it is frequently used alongside CRP in rheumatologic and infectious settings.

Evidence & guidelines

Reviews of the test describe its biological basis, influencing factors, and comparison with CRP (Brigden, 1999; Gabay & Kushner, 1999), and the contrast in kinetics with CRP is discussed in the CRP literature (Pepys & Hirschfield, 2003). This entry summarizes that material at a reference level and is not a guideline.

History

Fåhraeus described the influence of plasma proteins on red-cell sedimentation in the early twentieth century, and Westergren standardized the measurement in 1921 in studies of pulmonary tuberculosis, giving the method that still bears his name. The ESR became one of the earliest routine laboratory markers of inflammation and remains in use a century later, increasingly complemented by CRP.

Debates

How should the ESR be used relative to CRP?

Because CRP responds faster and more directly to inflammation while the ESR is slower and more affected by non-inflammatory factors, there is ongoing discussion about when each adds value and whether they should be ordered together.

Key figures

• Alf Vilhelm Albertsson Westergren
• Robin Fåhraeus
• Malcolm Brigden

Seminal works

• westergren-1921
• brigden-1999

Frequently asked questions

What makes the erythrocyte sedimentation rate increase?

It rises mainly when inflammation raises plasma fibrinogen and similar proteins, which cause red cells to aggregate into rouleaux that settle faster; the ESR therefore reflects the plasma protein environment rather than measuring one specific marker.

Why might the ESR be normal when CRP is high, or vice versa?

The two markers have different kinetics and drivers: CRP changes within hours and tracks current inflammation closely, while the ESR changes over days and is also influenced by anaemia, age, sex, and immunoglobulins, so they can diverge.