White Blood Cell Disorders

WBC Overview - Count Control

• WBC production (leukopoiesis) regulated by growth factors (e.g., G-CSF) & cytokines, responding to stimuli (infection).

• Normal WBC Counts & Differentials (Approximate Ranges in Children):

  Age	Total WBC (x10³/µL)	Neutrophils (%)	Lymphocytes (%)
  Newborn	9-30	40-80	20-40
  1-12 mo	6-17.5	20-45	45-70
  1-6 yr	5-15.5	25-60	35-65
  >6 yr	4.5-13.5	35-70	25-50

• Key Definitions: (ANC: Absolute Neutrophil Count)

  • Leukocytosis: ↑ WBC count (age-specific).
  • Leukopenia: ↓ WBC count (age-specific).
  • Neutrophilia: ↑ ANC (age-specific).
  • Neutropenia: ANC < 1500/µL (Mild: 1000-1500; Moderate: 500-999; Severe: < 500/µL).
  • Lymphocytosis: ↑ Lymphocytes (age-specific).
  • Lymphopenia: ↓ Lymphocytes (age-specific).
  • Eosinophilia: Eosinophils > 500/µL.

⭐ Age-related variations in WBC counts are crucial; lymphocyte predominance is normal in early childhood (up to 4-6 years), shifting to neutrophil predominance later.

Neutrophil Disorders - Neutro-Navigators

• Neutropenia: Absolute Neutrophil Count (ANC) < 1500/µL; severe if ANC < 500/µL.
  • Causes: Congenital (e.g., Kostmann syndrome, cyclic neutropenia); acquired (e.g., drugs, infections, autoimmune).
• Neutrophilia: Increased neutrophils.
  • Causes: Infections, inflammation, stress.
• Functional Neutrophil Disorders:
  • Chronic Granulomatous Disease (CGD): Defect in NADPH oxidase. Recurrent infections with catalase-positive organisms (📌 e.g., S. aureus, Aspergillus, Serratia). Diagnosis: Dihydrorhodamine (DHR) test or Nitroblue Tetrazolium (NBT) test.
  • Leukocyte Adhesion Deficiency (LAD): Types I, II, III. Delayed umbilical cord separation, recurrent non-purulent bacterial infections.

⭐ Chronic Granulomatous Disease (CGD) is most commonly X-linked recessive and diagnosed by an abnormal dihydrorhodamine (DHR) flow cytometry test or nitroblue tetrazolium (NBT) dye test, showing impaired phagocytic oxidative burst.

Lymphocyte Disorders - Lympho-Legends

• Lymphocytosis: ↑ Lymphocytes
  • Definition: Age-dependent. Infants >9000/µL, older children >7000/µL.
  • Causes:
    • Viral: Infectious Mononucleosis (EBV, CMV) - Downey cells (atypical lymphocytes).
    • Bacterial: Pertussis (marked ↑, normal morphology), TB.
    • Malignancies: Acute Lymphoblastic Leukemia (ALL).
• Lymphopenia: ↓ Lymphocytes
  • Definition: Age-dependent. Older children <1500/µL.
  • Causes: Immunodeficiencies (SCID, DiGeorge), HIV, drugs, malnutrition.
• Severe Combined Immunodeficiency (SCID):
  • Presentation: Failure to thrive (FTT), recurrent severe infections, absent thymic shadow.
  • Key Types: X-linked, ADA deficiency.

⭐ Infectious Mononucleosis (caused by EBV) is characterized by fever, pharyngitis, posterior cervical lymphadenopathy, splenomegaly, and atypical T lymphocytes (Downey cells) on the peripheral blood smear.

Eosinophil & Other Disorders - Eosino-Enigmas

• Eosinophilia: Absolute eosinophil count >500/µL.
  • Causes 📌 NAACP: Neoplasm, Allergy/Asthma, Addison's disease, Collagen vascular diseases, Parasitic infections.
  • Hypereosinophilic Syndrome (HES): Persistent eosinophilia >1500/µL with end-organ damage.
• Monocyte Disorders:
  • Monocytosis: ↑ monocytes. Causes: Chronic infections (e.g., TB), IBD, malignancies.
  • Langerhans Cell Histiocytosis (LCH): Rare, clonal proliferation of Langerhans cells; can affect bone, skin.
• Basophil Disorders:
  • Basophilia: ↑ basophils. Rare. Causes: CML, allergic reactions, hypothyroidism.

⭐ The mnemonic 'NAACP' (Neoplasm, Allergy/Asthma, Addison's disease, Collagen vascular diseases, Parasites) is a useful tool for remembering the common causes of eosinophilia in children.

High‑Yield Points - ⚡ Biggest Takeaways

• Neutropenia: ANC < 1500/µL (severe < 500/µL). Kostmann syndrome (SCN) ↑ AML risk.
• LAD-1: CD18 defect, delayed cord separation, recurrent non-purulent infections, marked neutrophilia.
• Chédiak-Higashi: AR; partial albinism, recurrent infections, giant granules in WBCs.
• CGD: Defective NADPH oxidase, recurrent catalase-positive infections. DHR/NBT test.
• EBV (Mononucleosis): Fever, pharyngitis, lymphadenopathy, atypical lymphocytes (Downey cells).
• ALL: Most common childhood cancer; lymphoblasts in blood/marrow, pancytopenia.