**6. Laboratory diagnosis**

The laboratory testing is essential to diagnose and delineate the immunologic defects of PIDs. Patients with clinical suspicion should be further investigated for the response of innate immunity and adaptive immunity [33, 34]. **Table 4** listed the most common tests used for initial screening of PIDs.

#### **6.1 Evaluation of humoral immunity**

Measurement of serum immunoglobulins is the first-line test for evaluating B-lymphocyte functions. Quantitative measurements of IgG, IgA, IgM, and IgE will identify either hypogammaglobulinemia or deficiency of an individual class of immunoglobulins. Evaluation of IgG subclasses may be required when a patient has strong implication of humoral immunodeficiency but the total IgG is normal. To be mindful, the results of immunoglobulin quantitation must be interpreted with appropriate age-specific ranges. Assessment of antibody responses to immunization with protein antigens (e.g., tetanus or diphtheria toxoids) and polysaccharide antigens (e.g., pneumococcal capsular) is another way to evaluate humoral immunity,


**Table 4.** *Initial laboratory tests for PIDs.*

although note is to be taken that live viral vaccines must be restricted to a patient with underlying immunodeficiency [35].
