The need to evaluate immunologic function has become a part of the standard practice of clinical medicine, resulting at least in part from the secondary immunodeficiency produced by human immunodeficiency virus (HIV) infection. In addition, since the early 1990s the molecular basis of primary immunodeficiency disorders has evolved, with now more than 200 genetic defects identified impacting host defense and an expanded range of clinical phenotypes associated with the resulting immune dysfunction. This chapter presents the general methods available to assess immune function, linking these to the clinical infectious history that is suggestive of specific types of immunodeficiency.

The primary clinical problem that sets the stage for initiating an immunologic evaluation is a history of increased susceptibility to infection. In general, the specific characteristics of the recurrent and/or chronic infections, including organism(s), site(s), frequency, and response to therapy provide critical insights into the most likely type or category of immunodeficiency.

The primary clinical problem that sets the stage for initiating an immunologic evaluation is a history of increased susceptibility to infection. In general, the specific characteristics of the recurrent and/or chronic infections, including organism(s), site(s), frequency, and response to therapy provide critical insights into the most likely type or category of immunodeficiency.

Defects in adaptive immunity involving anti-body production (humoral immunity) most typically lead to recurrent infections with high-grade encapsulated extracellular bacteria such as Haemophilus influenzae (often untypeable) and Streptococcus pneumoniae usually affecting the sinopulmonary tract.