Erythrocyte Sedimentation Rate

The erythrocyte sedimentation rate measures how far red cells fall in 1 hour in a vertical column of anticoagulated blood. Sedimentation increases when fibrinogen and immunoglobulins neutralise the negative surface charge of red cells and promote rouleaux. It is a non-specific indicator of the acute phase response.

It is most useful in giant cell arteritis, polymyalgia rheumatica and the monitoring of established inflammatory disease. It is a poor screening test in asymptomatic people.

Method. The Westergren method uses EDTA or citrate blood in a 200 mm column with a 1-hour reading at 18 to 25 °C. Test within 4 hours at room temperature, or within 24 hours at 4 °C. Automated alternatives are calibrated to the Westergren method.

Reference values (mm/h).

A simple age formula for the upper limit is age divided by 2 in men, and (age plus 10) divided by 2 in women.

Markedly raised (over 100 mm/h). Usually indicates serious disease: giant cell arteritis, polymyalgia rheumatica, multiple myeloma, endocarditis, osteomyelitis, tuberculosis, malignancy, systemic vasculitis, connective tissue disease, renal disease.

Moderately raised. Infection, inflammation, anaemia, pregnancy, older age, female sex, obesity, nephrotic syndrome, raised immunoglobulins or fibrinogen, hypercholesterolaemia.

Lowered or falsely low. Polycythaemia, sickle cell disease, hereditary spherocytosis, microcytosis, hypofibrinogenaemia, heart failure, severe leucocytosis, high dose corticosteroids.

Kinetics. It rises over 24 to 48 hours after an inflammatory insult and falls slowly over days to weeks. CRP rises and falls faster.

Critical findings needing immediate action. A raised ESR with new headache, jaw claudication, visual symptoms or scalp tenderness in a person over 50 years needs urgent assessment for giant cell arteritis. The ESR is normal in a minority of patients with biopsy proven disease.

Pitfalls.

• Tilted tubes, vibration, a delay over 4 hours, high temperature and air bubbles alter results.
• Anaemia raises and polycythaemia lowers the rate.
• A normal ESR does not exclude infection, malignancy or vasculitis.
• Low sensitivity and specificity limit use in asymptomatic screening.

Special groups. Pregnancy raises the ESR, with third trimester values commonly 40 to 70 mm/h. Older adults have higher baseline values, and children have lower values.

Follow up tests. C-reactive protein, plasma viscosity, full blood count, serum protein electrophoresis, immunofixation, temporal artery biopsy, blood cultures.