Immunofluorescence Labeling Indices in Myeloma and Related Monoclonal Gammopathies

We measured plasma cell labeling indices (LI) in 52 patients with monoclonal gammopathies. Cytoplasmic reactivity with polyspecific or κ- and λ-specific light chain anti-Ig reagents identified monoclonal plasma cells, plasmablasts, and lymphocytoid plasma cells. Among newly diagnosed untreated patients, a high immunofluorescence LI distinguished those with multiple myeloma (MM) from those with stable monoclonal gammopathies (P<0.002). Among treated patients with MM, those in the plateau phase of the disease had low LI, whereas patients in the relapse phase or early in treatment had high LI. The immunofluorescence LI correctly classified three more patients with newly diagnosed MM than did the tritiated thymidine LI technique. LI specific for the neoplastic plasma cells resulted in excellent discrimination of patients with active disease. Because results are easily and rapidly obtained, this technique is useful clinically.