The serum heavy/light chain immunoassay: A valuable tool for sensitive paraprotein assessment, risk, and disease monitoring in monoclonal gammopathies

ObjectiveThe heavy/light chain (HLC)-immunoassay quantifies light chain types of each immunoglobulin class in patients with monoclonal gammopathies. MethodsWe assessed 147 consecutive patients with different forms and stages of plasma cell dyscrasias (PCD) who received standard tests (serum and urine protein electrophoresis [SPEP, UPEP], immunofixation [IFE], serum-free light chain [SFLC]), and HLC-immunoassay. Patients with multiple myeloma (MM, n=102), smoldering MM (SMM, n=5), monoclonal gammopathy of undetermined significance (MGUS, n=28), and Waldenstrom's macroglobulinemia (WM, n=12) were included. ResultsWe verified a significant correlation between HLC- and standard monoclonal protein (mp)-parameters, and HLC-increases with higher disease stage and unfavorable remission status. In patients with difficult to quantify mp, more abnormal HLC- than SPEP-, immunoglobulin-, or SFLC-results were found. In WM, a pathological HLC /-ratio and M-component were observed in 95% and 58%, respectively. In 21/28 MGUS and 5/5 SMM patients, HLC /-ratios were abnormal. Testing different HLC cutoffs, patients with extreme HLC values showed impaired progression-free survival (PFS). ConclusionsDespite the fact that different PCD patients were included, the assessment of the HLC-immunoassay in MGUS, SMM, MM, and WM, our comparison with standard mp-assays, and relevant PFS differences may excite future applications, which should be confirmed in prospective multicenter trials.