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
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