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Lymphocytosis
Overview

Lymphocytosis, or a high lymphocyte count, is an increase in white blood cells called lymphocytes. Lymphocytes are an important part of the immune system. They help fight off diseases, so it’s normal to see a temporary rise in the number of lymphocytes after an infection.1

 

A count significantly higher than 3,000 lymphocytes in a microliter of blood is generally considered to be lymphocytosis in adults. In children, the threshold for lymphocytosis varies with age. It may be as high as 9,000 lymphocytes per microliter. The exact thresholds for lymphocytosis may vary slightly from one lab to another.1

Symptoms

With a lymphocyte count that is higher than would normally be expected there are few, if any, symptoms. It’s usually a harmless, temporary situation, as can occur after an illness. But it may represent something more serious, such as a blood cancer or a chronic infection.1

Causes and Risk Factors
  • Infection (bacterial, viral, other)
  • Cancer of the blood or lymphatic system
  • An autoimmune disorder causing ongoing (chronic) inflammation1
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