The CD19 test is a specialized blood test that measures the percentage and absolute number of CD19-positive B lymphocytes in your immune system. CD19 is a key surface biomarker found exclusively on B cells, which are responsible for producing antibodies to fight infections.
Clinicians primary use this test to monitor and evaluate immune deficiencies, autoimmune disorders, and blood cancers like chronic lymphocytic leukemia (CLL) or non-Hodgkin lymphoma. It is also crucial for tracking patient response and immune system recovery during targeted immunotherapy treatments, such as anti-CD19 CAR-T cell therapy or targeted monoclonal antibody drugs like rituximab.