Pathology dictionary

What is lymphocytosis?

Lymphocytosis is a word pathologists use to describe an increased number of specialized immune cells called lymphocytes either in the blood or inside an organ. Organs that commonly show lymphocytosis include the stomach, small bowel, and colon.

Lymphocytes normally help the body fight off infections caused by viruses and bacteria. However, increased numbers of lymphocytes inside of a tissue can also cause injury.

Because there are many things that can cause lymphocytosis, it is not a diagnosis by itself. Your doctors will use the information found in your pathology report along with other information about you to determine the cause of the lymphocytosis. The most common causes of lymphocytosis are listed below.

Causes of lymphocytosis in the blood

  • Recent viral infection
  • Trauma
  • Reaction to a new medication
  • Leukemia or lymphoma
  • Prior removal of the spleen
  • Medical conditions associated with inflammation such as arthritis or lupus

Causes of lymphocytosis in the stomach, small bowel, and colon

  • Celiac disease (gluten sensitive enteropathy)
  • Non-gluten sensitivity
  • Medications
  • Inflammatory bowel disease
  • Immune system disease
  • Microscopic colitis
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