Lymphocyte Count

Aka: Lymphocyte Count, Lymphocyte, Lymphocytosis

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II. Characteristics

  1. Forms in Bone Marrow from Lymphoblasts (which are in turn derived from stem cells)
  2. Function: Primary source of viral defense and Antibody
    1. Adaptive Immunity (learned response)
      1. B-Lymphocyte
        1. Humoral Immunity with Antibody against extracellular Antigens
      2. T-Lymphocyte
        1. Cellular Immunity via T-Helper/CD4+ Cells and T-Cytotoxic/CD8+ Cells
    2. Innate Immunity
      1. Natural Killer Cells (NK cells)
        1. Lymphocytes providing immediate protection against Intracellular Bacteria, viruses, cancer cells
  3. Morphology on Blood Smear
    1. Mononuclear Leukocytes (same class as Monocytes)
    2. Small cells with minimal cytoplasm

III. Labs: Normal

  1. Percentage Lymphocytes: 15-40% of White Blood Cells
  2. Total Lymphocytes: 800-2600/mm3
  3. Total T Lymphocytes: 800-2200/mm3
    1. T helper Cells: >400/mm3
    2. T suppressor Cells: 250-750/mm3
    3. Helper Cell to Suppressor Cell ratio: >0.9
    4. CD2 Percentage of Lymphocytes: 65-85%
    5. CD4 Percentage of Lymphocytes: 45-75%

IV. Causes: Increased (Lymphocytosis)

  1. Increased Absolute Lymphocyte Count (>4500/mm3)
    1. Non-activated Lymphocytes
      1. Influenza
      2. Pertussis
      3. Tuberculosis
      4. Mumps
      5. Varicella
      6. Herpes Simplex Virus
      7. Rubeola
      8. Brucellosis
      9. Fungal infection
      10. Rickettsial infection
      11. Chronic Lymphocytic Leukemia
      12. Acute Lymphoblastic Leukemia
    2. Activated Lymphocytes (Atypical lymphocytes)
      1. Cytomegalovirus Infection
      2. Infectious Mononucleosis
      3. Infectious Viral Hepatitis
      4. Toxoplasmosis
      5. Syphilis
      6. Post-transfusion
      7. Beta Streptococcus
      8. Medication
        1. Mephenytoin
        2. Dilantin
        3. Para-Aminosalicylic Acid
  2. Increased Relative Lymphocyte Count (>40% of total)
    1. Normal finding in children under age 2 years
    2. Acute stage of Viral Infection
    3. Connective Tissue Disease
    4. Hyperthyroidism
    5. Addison's Disease
    6. Splenomegaly

V. Causes: Decreased

  1. AIDS
  2. Bone Marrow suppression
  3. Aplastic Anemia
  4. Neoplasms
  5. Steroids
  6. Adrenocortical hyperfunction
  7. Neurologic Disorders
    1. Multiple Sclerosis
    2. Myasthenia Gravis
    3. Gullain Barre Syndrome

VI. Evaluation: Lymphocytosis (Lymphocytes >4500/mm3)

  1. See Leukocytosis
  2. History and potential causes
    1. Contagious contacts
    2. Immunization history
  3. Diagnostics (consider)
    1. Viral specific studies (e.g. Monospot)
    2. Chest XRay

VII. References

  1. Saiki in Friedman (1991) Medical Diagnosis, p. 227
  2. Abramson (2000) Am Fam Physician 62(9):2053-60 [PubMed]
  3. Riley (2015) Am Fam Physician 92(11):1004-11 [PubMed]

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