Evaluation of primary immunodeficiency disease in children.

One in 2,000 children younger than 18 years is thought to have a primary immunodeficiency disease. Antibody, combined B-cell and T-cell, phagocytic, and complement disorders are the most common types. Children with these diseases tend to have bacterial or fungal infections with unusual organisms, or unusually severe and recurrent infections with common organisms. A family history of primary immunodeficiency disease is the strongest predictor of a person having this type of disease. When an immunodeficiency disease is suspected, initial laboratory screening should include a complete blood count with differential and measurement of serum immunoglobulin and complement levels. The presence of lymphocytopenia on complete blood count suggests a T-cell disorder, whereas a finding of neutropenia suggests a phagocytic disorder. Abnormal serum immunoglobulin levels suggest a B-cell disorder. Abnormalities on assay of the classic or alternative complement pathways suggest a complement disorder. If laboratory results are abnormal, or if clinical suspicion continues despite normal laboratory results, children should be referred for further evaluation. Human immunodeficiency virus infection should also be considered, and testing should be performed, if appropriate; this infection often clinically resembles a T-cell disorder.