[Laboratory diagnosis of immune deficiency]

Highly specialized, state-of-the-art diagnostic tests are available for identifying congenital and acquired immune defects. These methods should only be resorted to when less complicated means have created suspicion of an immune defect. The case history, including the family history, represents the core of the diagnostic procedure. Initially, only simple clinical investigations are indicated. These should enable the physician to exclude or delimit a defect in the immune system which then can be defined more closely by specific tests. Screening includes clinical chemistry (erythrocyte sedimentation rate, total serum protein, serum electrophoresis, C-reactive protein, blood count including differential blood count, ferritin, urine analysis, and a quantitative assay of the immunoglobulins A, G and M), bacteriological, serological, and radiological investigations, and finally skin tests with recall antigens. Thereby, it is usually possible to reliably detect primary B cell defects with humoral antibody deficiency syndromes. Lymphocyte subset counts, immunoelectrophoresis, and bone marrow biopsy are necessary for the differential diagnosis, or for the confirmation, of malignant lymphatic proliferation, especially in adults. IgG subclass defects as well as granulocyte dysfunction and complement defects must be excluded in patients who are susceptible to bacterial infection despite normal immunoglobulin concentrations. In suspected cases of primary or secondary (HIV, cytomegalovirus, Epstein-Barr virus) T cell defects, lymphocyte subset counts and, where applicable, T cell function tests are indicated. The majority of secondary immunodeficiency syndromes, in which the primary disease is known, do not currently require specialized diagnosis. Nevertheless, monitoring of the lymphocyte subsets in HIV-positive patients has already become standard practice in health care (for evaluating the prognosis and deciding on the therapy).