Which test is the most useful way to evaluate the response to treatment for multiple myeloma?

The measurement of serum-free light chains is the most useful method for evaluating the response to treatment in multiple myeloma due to their direct association with the activity of the disease. In multiple myeloma, abnormal plasma cells produce excess light chains—either kappa or lambda—that can circulate freely in the serum. Monitoring these free light chains provides immediate insight into the tumor burden and helps to assess treatment efficacy over time.

Serum-free light chain assay has become a crucial tool in this context because it can detect minimal residual disease and changes in the plasma cell population that traditional methods may not capture adequately. This sensitivity is especially critical in tracking the effectiveness of treatment protocols and making necessary adjustments in therapy.

While other methods, such as measuring total immunoglobulin or assessing urinary light chains, provide some information related to multiple myeloma, they may not be as sensitive in detecting early changes in the disease state or in assessing response after treatment. Furthermore, capillary electrophoresis of M-protein recurrence can be useful too, but it primarily focuses on the detection of M-protein levels rather than the overall disease burden represented by free light chains. Hence, the measurement of serum-free light chains stands out as the most effective choice for evaluating treatment response in patients with