A CD25 test is a specialized laboratory assay that measures expression of the CD25 protein, the alpha chain of the interleukin-2 (IL-2) receptor. Predominantly expressed on activated T cells, regulatory T cells (Tregs), and certain neoplastic lymphocytes, this test is commonly performed using flow cytometry or immunohistochemistry on blood, bone marrow, or tissue samples.
It serves as a critical diagnostic tool for identifying specific hematologic malignancies, such as adult T-cell leukemia/lymphoma (ATLL) and hairy cell leukemia. Additionally, elevated CD25 levels assist in monitoring autoimmune diseases, organ transplant rejection, and systemic inflammatory conditions like hemophagocytic lymphohistiocytosis.