Specific antibody titers after childhood vaccination (tetanus, diphtheria, Haemophilus influenzae type b, or Streptococcus pneumoniae vaccines) reflect the capacity of the immune system to synthesize specific antibodies and to develop memory B cells. If titers are low, immunization with a specific vaccine and titers obtained 4 to 6 weeks later confirm response to the immunization. Poor response to bacterial polysaccharide antigens is normal before 24 months of age but is also associated with IgG subclass deficiency or specific antibody deficiency. The development of protein-conjugate polysaccharide vaccines has prevented infections with these organisms in early childhood. Antibody responses to the S. pneumoniaeserotypes found in the 23-valent polysaccharide vaccine, but not in the conjugate vaccine, can be used to test antibody responses to polysaccharide antigens.
Delayed-type hypersensitivity skin tests to protein antigens such as tetanus, diphtheria, Candida, or mumps demonstrate the presence of antigen-specific T cells and functional antigen-presenting cells. If delayed-type hypersensitivity skin test results are negative, patients should receive a booster vaccination and be retested 4 weeks later.
Complete blood count, including hemoglobin, differential white blood cell count and morphology, and platelet count Radiographs to document infection in chest, sinus, mastoids, and long bones, if indicated by clinical history
Cultures, if appropriate
Quantitative immunoglobulin levels: IgG, IgA, IgM, IgE, Isohemagglutinin titers (anti-A, anti-B, measures IgM function) Specific antibody levels:
Protein antigens: diphtheria, tetanus Protein-conjugated antigens: Haemophilus influenzae, Streptococcus pneumoniae (conjugate vaccine)
Polysaccharide antigens: S. pneumoniae (unconjugated vaccine) B-cell numbers and subsets by flow cytometry
Delayed hypersensitivity skin tests (Candida, tetanus toxoid, mumps): measure T-cell and macrophage function T-cell and NK cell numbers and subsets by flow cytometry
T-lymphocyte functional analyses (mitogen responses, cytokines) NK cell cytotoxicity assays
Nitroblue tetrazolium dye test/dihydrorhodamine 123 using flow cytometry Staphylococcal killing, chemotaxis assay Myeloperoxidase stain
Total hemolytic complement CH50: measures classical and common pathway activity
AH50: measures alternative and common pathway activity Levels of individual complement components
NK, Natural killer.
Lymphocyte phenotyping by flow cytometry enumerates the percentage and absolute numbers of T-cell, B-cell, and NK-cell subsets. Flow cytometry can also test for the presence of surface proteins that are necessary for normal immunity, such as major histocompatibility complex molecules or adhesion molecules, as well as intracellular analysis of signaling proteins and cytokines. T-cell proliferation assays to mitogens (phytohemagglutinin, concanavalin A, or pokeweed mitogen) or antigens (tetanus toxoid or Candida) are in vitro assays that confirm the capacity of T cells to proliferate in response to a nonspecific stimulus (mitogens) or the presence of antigen-specific memory T cells (antigens). Such presence requires prior vaccination (tetanus) or exposure (Candida)to the antigen. Tests for cytokine synthesis or expression of activation markers by T cells may be performed in specialized research laboratories and can help identify defects in T-cell function when, despite present T cells, the clinical history suggests a T-cell disorder.