Common Variable Immunodeficiency
Utility: 1) Diagnostic screen for common variable immunodeficiency (CVID).
2) Assess B cell response to immunotherapeutics.
3) Assess B cell subset reconstitution post-stem cell or bone marrow transplant.
Specimen: 4 - 10 mL peripheral blood in sodium heparin (green top).
CPT codes: 86359, 86360, 86355, 86357, 88184, 88185 x 10, 88188.
Clinical indication/general description
CVID is characterized by a low serum IgG and either a low IgA, a low IgM or both a low IgA and IgM along with an impaired ability to make specific antibodies in response to immunization. CVID may occur at any age and such patients have recurrent respiratory tract infections in particular with encapsulated bacteria and Mycoplasma sp. B cell numbers may be normal or decreased and T cell numbers also may be reduced. Patients with CVID are at increased risk to develop granulomatous or lymphocytic interstitial lung disease (GLILD), autoimmunity (such as autoimmune thrombocytopenic purpura or autoimmune hemolytic anemia) and lymphomas.
The CVID assay analyzes B cell maturation that occurs in a sequential immunophenotypic pattern (illustrated below). B cells that are naïve (antigen inexperienced) do not express CD27. Upon engagement with antigen, B cells express CD27 and are termed memory B cells. Memory B cells are further classified as unswitched memory B cells (express CD27 and IgD) and switched memory B cells (express CD27 but do not express IgD). Patients with CVID that have a markedly reduced number of switched memory B cells are at increased risk to have a more severe clinical phenotype and to develop GLILD. Low numbers of switched memory B cells also can be seen in other disorders affecting B cell maturation, such as hyper-IgM syndrome.