ESR blood test: normal range explained

ESR measures how quickly red blood cells (erythrocytes) sink to the bottom of a tall, thin tube of blood. When there is inflammation in the body, proteins make the cells clump, and clumps sink faster, so the distance they fall in one hour, in mm/hr, rises.

The usual method is the Westergren method, which Testing.com calls the gold standard, and reports often print ESR (Westergren) or ESR 1st hour. ESR is a non-specific test: it shows that inflammation may be present but not where it is or what is causing it.

Doctors order ESR when symptoms suggest a condition that causes inflammation, and to follow one that is already known. MedlinePlus lists headaches, unexplained fever or weight loss, joint stiffness, neck or shoulder pain and loss of appetite among the symptoms, and arthritis, vasculitis, infections and inflammatory bowel disease among the conditions.

It is often ordered with CRP, which MedlinePlus says gives more information, and it can show whether an illness is responding to treatment. MedlinePlus is clear that ESR is not used to diagnose a specific disorder on its own.

ESR shifts with age, sex and several everyday states, which is why labs print more than one limit.

• Age and sex: the printed limit rises with age and is higher for women, so the row that applies to you matters.
• Pregnancy raises ESR, especially in the second and third trimesters, and the menstrual cycle can affect it.
• Anaemia raises ESR and makes it less reliable; Testing.com says severe anaemia makes the test unreliable.
• Obesity, regular alcohol use and exercise are listed as factors that can affect the result.
• Medicines: corticosteroids and NSAIDs can lower ESR, while oral contraceptives, heparin and some blood pressure medicines can raise it.
• Kidney disease, thyroid disease and some cancers are listed causes of a higher ESR, while polycythaemia and sickle cell disease lower it.