The Plasma Cell Labeling Index: A Valuable Tool in Primary Systemic

> 0%. Of the 46 patients with an elevated LI. 1 9 (41 %) had multiple myeloma as compared with three (4%) of the 79 patients with an LI = 0 (P 0. as compared with ten (13%) of 79 T HE PLASMA CELL labeling index (LI) probes the biology of the plasma cell.’ This test is capable of recognizing plasma cells actively synthesizing DNA and can, therefore, differentiate proliferative from nonproliferative cells.2 The plasma cell LI has been repeatedly shown to be clinically useful in the classification and diagnosis of monoclonal gammopathy of undetermined significance, multiple myeloma and its plasmablastic subset, as well as smoldering multiple myeloma.3’4 The plasma cell LI also provides useful information about prognosis and the need for therapy at different times in the course of the disease.5 Primary amyloidosis (AL) is a plasma cell dyscrasia that shares many features with myeloma.6 Patients with AL typically have a monoclonal protein in their serum or urine and bone marrow plasmacytosis. Sometimes, diagnostic confusion arises when the two coexist in the same patient. Because AL is an uncommon disorder, no study of the basic kinetics of the plasma cell has been undertaken. To learn about the plasma cell kinetics and to assess clinical utility, we studied the LI in patients with AL. We wished to address whether the LI had any value in predicting response or