Lymphocytosis · What It Is, Causes, Signs and Symptoms, and More

Lymphocytosis refers to an increased number of lymphocytes in the bloodstream. Lymphocytes are a type of white blood cell that plays an important role in the immune system and helps in fighting off bacterial and viral infections. In lymphocytosis, high lymphocyte count in the blood may be suggestive of an evolving infection, an underlying systemic disorder (e.g., leukemia, lymphoma), or an iatrogenic cause (e.g., medication-induced hypersensitivity reactions). 

Lymphocytosis is often detected incidentally and therefore, signs and symptoms may be nonspecific and can include fever, tachycardia, malaise, night sweats, and lymphadenopathy. Unintentional weight loss in the setting of an infection or neoplastic process may also be present. In particular viral infections, like Epstein-Barr virus, splenomegaly may be seen. In the case of a suspected drug hypersensitivity reaction, a rash may be present.  Lymphocytosis caused by an acute condition (e.g., infection) typically resolves within one to two months after the underlying infectious process has cleared. A longer duration of lymphocytosis raises concerns for an underlying malignant process.

Lymphocytosis is often detected incidentally using a laboratory blood test called a complete blood count (CBC) with a differential. The abnormal CBC and differential count are often repeated to exclude laboratory error. A CBC with differential quantitatively measures the white blood cell count in the body along with the breakdown of various subtypes of white blood cells including the lymphocyte count. A surgical and medical history (e.g., recent medication changes) and physical exam to assess lymphadenopathy, splenomegaly, or rash can help determine the underlying etiology and whether the observed lymphocytosis is physiologic or pathologic. Additionally, a peripheral blood smear is a qualitative way of assessing lymphocyte morphology. For example, normal-appearing or reactive lymphocytes (i.e., large lymphocytes with abundant basophilic cytoplasm) are often seen in viral infections whereas binucleate (i.e., two nuclei) lymphocytes are suggestive of a lymphoproliferative disorder. Lastly, a specialized blood test known as flow cytometry may be ordered if there is suspicion of acute leukemia, or if the absolute lymphocyte count is >30,000 cells/microL without a known diagnosis.

Management of lymphocytosis includes treating the underlying cause. In the case of bacterial infections, antibiotic treatment can shorten the symptom burden and duration of illness. Viral infections are typically self-limiting and treatment is mainly supportive care with fluids. For drug hypersensitivity reactions, cessation of the offending medication is the mainstay of treatment along with supportive care measures (e.g., fluid and electrolyte supplementation). For lymphoproliferative diseases, a variety of treatments including chemotherapy, radiation therapy, or stem cell transplantation can be considered. Referral to a hematology specialist may also help manage complex, hematologic disorders resulting in lymphocytosis.

Lymphocytosis refers to an increased number of lymphocytes in the bloodstream. Lymphocytes are a type of white blood cell that plays an important role in the immune system and helps in fighting off bacterial and viral infections. Lymphocytosis can occur due to a variety of etiologies including stress, infection, systemic illness, or drug hypersensitivity reactions. Signs and symptoms of lymphocytosis may be nonspecific and may include fever, tachycardia, malaise, night sweats, and lymphadenopathy. Lymphocytosis is diagnosed using a laboratory blood test called a complete blood count (CBC) with a differential. A thorough review of symptoms, medical history, and physical exam can all help determine the underlying etiology causing lymphocytosis. Treatment is aimed at managing the underlying cause.