Etiology

Diagnosis

Work-Up of Suspected Immunodeficiency in the Child

• Complete Blood Count (CBC) with Manual Differential (see Complete Blood Count, [[Complete Blood Count]])
  • Absolute Lymphocyte Count
    • Normal absolute lymphocyte count makes the diagnosis of a T-cell defect unlikely
  • Absolute Neutrophil Count
    • Normal absolute neutrophil count excludes the diagnosis of congenital/acquired neutropenia
    • Normal absolute neutrophil count (usually) excludes the diagnosis of leukocyte adhesion deficiency syndromes: elevated absolute neutrophil counts are present between infections
  • Howell-Jolly Bodies
    • Absence of Howell-Jolly bodies excludes the diagnosis of asplenia
  • Platelet Count
    • Normal platelet count excludes the diagnosis of Wiskott-Aldrich syndrome
• Erythrocyte Sedimentation Rate (ESR) (see Erythrocyte Sedimentation Rate, [[Erythrocyte Sedimentation Rate]])
  • Normal ESR makes diagnosis of chronic bacterial/fungal infection unlikely
• Human Immunodeficiency Virus (HIV) Testing (see Human Immunodeficiency Virus, [[Human Immunodeficiency Virus]])
• Screening Tests for Complement Deficiency
  • CH50: genetic complement deficiencies are usually characterized by extremely low CH50 values
• Screening Tests of Phagocytic Defects
  • Absolute Neutrophil Count: as above
  • Respiratory Burst Assay
    • Nitroblue Tetrazolium (NBT): older test no longer used
    • Rhodamine Dye Test: currently used test in most labs
  • Flow Cytometry with Monoclonal Antibodies Against Leukocyte Adhesion Cell Surface Markers: CD18, CD11 (LAD1), CD15 (LAD2)
• Tests for T-Cell Defects
  • Absolute Lymphocyte Count: as above
  • Candida Albicans Intradermal Skin Test: most cost-effective test of T-cell function (as a positive test excludes all primary T-cell defects)
    • Patients <6 y/o: 0.1 ml of 1:100 dilution
    • Patients >6 y/o: 0.1 ml of 1:1000 dilution
    • Positive Test: at least 10 mm erythema + induration at 48 hrs (and that is greater than that at 24 hrs)
• Tests for B-Cell Defects
  • Diphtheria Antibody
  • Haemophilus Antibody
  • IgA: order first -> if low, then order IgG and IgM
    • Normal IgA excludes diagnosis of IgA deficiency and most of the permanent types of hypogammaglobulinemia (IgA is usually absent-very low in these conditions)
  • IgG
  • IgM
  • Isohemagglutinins (Antibodies to type A and B blood polysaccharide antigens)
    • May be absent normally in the first 2 years of life
    • Always absent if the patient is blood type AB
  • Pneumococcal Antibody
  • Tetanus Antibody

References

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