Laboratory features of selective IgM deficiency

Complete blood count

Total lymphocyte number may be normal or low

Other cell types normal

Total hemolytic complement (CH50) normal

Antibodies

IgM low or absent

IgG and IgA normal

IgE may be normal or mildly elevated (elevations may indicate presence of associated allergic diseases)

Flow cytometry of lymphocytes

CD4+ T cells may be low or normal

CD8+ T cells may be low or normal

B cells and NK cells normal

HIV testing negative

Response to vaccination

Response to pneumococcal polysaccharide vaccine (T cell-independent carbohydrate antigens) may be normal or impaired

Response to diphtheria/tetanus vaccine (T cell-dependent protein antigens) may be normal or impaired

IgM: immunoglobulin M; IgG: immunoglobulin G; IgA: immunoglobulin A; IgE: immunoglobulin E; NK: natural killer; HIV: human immunodeficiency virus.

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