Diagnosis of immunologic deficiency in childhood.

A defective host response may be responsible for recurring infections in certain children. Recognition of these defects may be important both therapeutically for the patient and for genetic counseling for the family. Family history, age of onset of illness and type of infecting agents may all point to one or another defect in host resistance. An initial evaluation for suspected immunologic disease may be rapidly accomplished and should include absolute neutrophil and lymphocyte counts, chest X-ray for a thymic shadow, Schick test for functional IgG antibodies and isohemagglutinin titers for functional IgM antibodies. Although serum protein electrophoresis is unreliable for diagnosis of most disorders of circulating antibodies, quantitation of the IgG, IgA and IgM antibody classes is generally available. More extensive studies may be carried out to further define defects in the cell-mediated immune system, in the various complement components, or in the ingestion and killing of bacteria by neutrophils.