Diagnosis of hairy cell leukemia by flow cytometry.

Flow cytometric immunophenotpying (FCI) is a vital tool in the diagnosis of hairy cell leukemia (HCL). HCL has a distinctive immunophenotype based upon staining with antibodies to CD5 (negative), CD10 (negative), CD23 (negative), CD20 (abnormally bright), CD22 (abnormally bright), CD11c (abnormally bright), CD25 (abnormally bright), CD103 (positive), and CD123 (positive). Due to this unique immunophenotype, FCI can differentiate malignant hairy cells from normal B-cells and other lymphoproliferative disorders, especially the morphologically similar hairy cell leukemia variant and splenic lymphoma with villous lymphocytes. FCI is extremely sensitive in the detection of minimal disease and is useful in monitoring response to therapy.