Differentiation of chronic lymphocytic leukemia from reactive lymphocytosis by the mouse red cell rosette assay

The differential diagnosis of chronic lymphocytic leukemia (CLL) from other neoplastic and nonneoplastic lymphocytoses may be difficult, even when optimal clinical and laboratory data are available. The mouse red cell (M) rosette assay has been valuable in distinguishing normal and lymphomatous lymphocytes from those of CLL. Not yet tested is the ability of this test to separate reactive (benign) lymphocytes from morphologically similar but neoplastic cells of CLL. In the present study, lymphocytes of 58 subjects with CLL, reactive lymphocytosis, and healthy controls were evaluated for M rosette formation, in addition to the usual B and T cell markers. Lymphocytes from patients with CLL showed a marked increase in the ability to form M rosettes in comparison to those from normal controls and patients with reactive lymphocytosis. The formation of M rosettes was a more reliable marker for CLL than surface membrane immunoglobulin.