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
- Absolute Lymphocyte Count
- 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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