The utility of flow cytometry for the diagnosis of primary immunodeficiencies.

Primary immunodeficiencies (PID) or inborn errors of immunity affect phenotype and/or function of one or more components of the immune system. The exponential growth of genetic analysis has enabled identification of known and novel mutations. However, genetic analysis continues to be expensive and is not easily accessible. Flow cytometry, on the other hand, has been well established for many years in clinical laboratories and its use for the analysis of immunodeficiencies is expanding. Surface, intracellular, and intranuclear proteins can easily be evaluated by flow cytometry, enabling both phenotypic and functional identification of specific cell populations and therefore facilitating the identification of a variety of PIDs. While genetic analysis provides a definitive diagnosis for PIDs, flow cytometry is necessary to confirm or establish the immune phenotype of a gene mutation. Furthermore, flow cytometry provides a rapid means to identify an immunological defect at a relatively low cost.