Lymphocyte surface marker studies in the diagnosis of unexplained lymphocytosis.

Fifty-six patients with unexplained lymphocytosis were investigated with a panel of antibodies to lymphocyte surface antigens. In 23 the distribution of cell surface markers suggested reactive lymphocytosis. The remaining 33 patients showed a distribution of cell surface markers that indicated or suggested a diagnosis of B-cell lymphoproliferative disease. Two illustrative case reports show how such studies performed early in the investigation of unexplained lymphocytosis may permit earlier diagnosis of the underlying mechanism.