Immune Defects

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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