Laboratory Investigation of Secondary Immunodeficiency

Although a knowledge of the cellular pathology underlying many secondary immunodeficiencies is essential to an understanding of the clinical presentation and management of these common conditions, the specific role of the diagnostic immunology laboratory is strictly limited in many of them. While basic biological mechanisms are not illustrated as clearly as they are in congenital disorders, the underlying defects in secondary immunodeficiency can generally be discerned. Even in AIDS and related conditions caused by the T lymphotropic retrovirus HTLV-III/LAV, immunological tests form only a part of the pattern recognition in diagnosis and are not pathognomonic; their relevance can only be established with reference to the clinical state. However, AIDS, with its precisely defined aetiology and its increasingly well-understood immunopathogenesis, has helped to clarify the relevance of different assays in both this and other diagnostic settings. The relative lack of specificity of such assays and the limitations inherent in the use of peripheral blood have been underlined by this remarkable disease. AIDS has highlighted the importance of defining the clinical context in which laboratory abnormalities are found.