Diagnostik primärer immundefekte: Vom klinisch-immunologischen phänotyp zur molekularen diagnose

The basic diagnostic assessment of primary immunodeficiencies should allow recognition of most life-threatening and common conditions. This consists of a microscopic differential blood count and determination of immunoglobulin levels of IgG, IgA, IgM and IgE. Patients with severe combined immunodeficiency (SCID) often, but not always, present with lymphopenia and lack of IgM. Patients with a persistent lack of IgG, IgA and/or IgM and antibodies against recall antigens beyond the second year of life are suspected of having common variable immunodeficiency (CVID) if secondary causes for immunoglobulin loss can be excluded. This basic work-up will identify only 40-50% of primary immunodeficiencies. Advanced diagnostic work-up is based on findings such as isolated pathogens, severity and course of infections, syndrome manifestations and signs of immune dysregulation. Advanced work-up aims to narrow down the defect to a specific part of the immune system on a phenotypic level. The precise description of the clinical and immunological phenotype is a prerequisite to identify the underlying molecular defect.