T and B lymphocyte enumeration in the diagnosis of lymphocyte-rich pleural fluids.

The presence of a monotonous population of small lymphocytes in effusions may be due to chronic lymphatic leukemia (CLL), malignant lymphoma of the small cell type (SLML) or a chronic inflammatory process, such as tuberculosis. In this report we provide evidence that the enumeration of T and B lymphocytes in such fluids may provide a reliable means of distinguishing between malignant and nonmalignant effusions. The mean percentage of T lymphocytes in th pleural effusions of ten patients wit nonmalignant diseases was 80.2, and the mean percentage of B lymphocytes was 7.4. In marked contrast, B cells predominated (mean, 83.3%) in the pleural effusions of patients with lymphoma or leukemia. Since the great majority of chronic lymphocytic lymphomas and leukemias are of B-cell origin, we conclude that effusions containing a large predominance of B cells have a high probability of being malignant. Those that contain a predominance of T cells are almost always benign, although one should always consider the rare occurrence of chronic lymphocytic lymphomas and leukemias of T-cell origin.