II. Definitions

  1. Leukocytosis
    1. White Blood Cell Count over 11,000/mm3 (non-pregnant adults)
    2. See White Blood Cell Count for normal White Blood Cell ranges based on age, pregnancy
  2. Leukemoid Reaction
    1. White Blood Cell Count 50,000 to 100,000/mm3
    2. Caused by serious infections (C. Diff, Sepsis), solid tumor, organ rejection
  3. Severe Leukocytosis (Hyperleukocytosis)
    1. White Blood Cell Count >100,000/mm3
    2. Associated with Leukemia or myeloproliferative disorder
    3. May be associated with Leukostasis (Hyperviscosity Syndrome) in AML (or CML in Blast Crisis)

III. Causes: Cell line specific causes

  1. See Neutrophilia (most common cause)
  2. See Lymphocytosis
  3. See Monocytosis
  4. See Eosinophilia (rarely causes Leukocytosis)

IV. Causes: Benign Syndromes

  1. Leukemoid Reaction
    1. WBC Count exceeds 50,000
    2. Cause not involving Bone Marrow
    3. Usually due to non-malignant cause
  2. Reactive Leukocytosis
    1. Fever
    2. Focal infectious signs
    3. Normal Platelet Count and Hemoglobin

V. Causes: Malignancy

  1. Acute Leukemia
    1. Thrombocytopenia
    2. Peripheral Smear with many immature cells (blasts)
    3. Marrow hypercellular with >30% blast cells
    4. Hyperuricemia
  2. Chronic Leukemia
    1. Normal Platelet Count and Hemoglobin

VI. Red Flags: Signs of Hematologic Malignancies or other Bone Marrow disorders

  1. History
    1. Bruising or Bleeding Diathesis
    2. Fatigue or weakness
    3. Fever >100.4 F (38 C)
    4. Night Sweats
    5. Unintentional Weight Loss
    6. Immunosuppression
  2. Exam
    1. Lymphadenopathy
    2. Bleeding, Ecchymosis, or Petechiae
    3. Lethargy
    4. Splenomegaly or Hepatomegaly
  3. Labs
    1. Anemia (reduced RBC Count or decreased Hemoglobin or Hematocrit)
    2. Thrombocytopenia or Thrombocytosis
    3. Peripheral Blood Smear abnormalities (monomorphic Lymphocytosis, immature cells)
    4. White Blood Cell Count >30,000/mm3 (or >20,000/mm3 after initial management)
      1. WBC Count >100,000/mm3 indicates urgent hematology consult
  4. References
    1. Racil (2011) Am J Hematol 86(9): 800-3 [PubMed]

VII. Evaluation: Leukocytosis

  1. Step 1
    1. Complete Blood Count with Platelets
      1. Confirm persistent WBC Count >11,000/mm3
    2. Consider known causes
      1. See WBC Count for normal ranges (increased in childhood, pregnancy)
      2. See specific WBC cell line increases (Neutrophilia, Lymphocytosis...)
  2. Step 2: Consider malignancy
    1. See Red Flags for Hematologic Malignancy as above
    2. Malignancy suspected
      1. Hematology-Oncology Consultation
      2. Peripheral Blood Smear
    3. Additional tests typically ordered by hematoology
      1. Bone Marrow Aspiration (critical in Acute Leukemia)
      2. Flow cytometry, cytogenic tests, molecular tests
  3. Step 3: Cell Line specific approach
    1. Neutrophilia (Neutrophils >7000/mm3)
      1. See Neutrophilia for evaluation
    2. Lymphocytosis (Lymphocytes >4500/mm3)
      1. See Lymphocytosis for evaluation
    3. Monocytosis (Monocytes >880/mm3)
      1. See Monocytosis for evaluation
    4. Eosinophilia (Eosinophils >500/mm3)
      1. See Eosinophilia for evaluation
    5. Basophilia (Basophils >100/mm3)
      1. See Basophilia for causes
      2. Consider malignancy
      3. Consider allergic condition

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