In this study, researchers compared intraindividual results of all three assays to determine the FLC (κ, λ, and the κ/λ ratio) for 47 MM patients. They determined that, while each assay has its benefits and drawbacks and all can be used for calculating FLC, the assays are not comparable and should not be used interchangeably as that can lead to misinterpretation in response assessment and overall disease course. Moreover, the thresholds for determining the disease state, which rely on the ratio of the involved FLC (iFLC; the type of FLC present in excess) with the uninvolved FLC (uiFLC; the type of FLC present at the normal level), are not comparable between the three assays. Thus, new threshold values are proposed for each assay.
The study found:
- Because the results of the iFLC versus uiFLC ratio thresholds were different depending on the test employed, unique thresholds should be defined for each assay. This is especially true in non-MM monoclonal gammopathies where diagnosis and treatment decisions are based solely on the iFLC/uiFLC ratio
- Although the concordance among tests for kappa FLC was very good, that for lambda FLC was only moderate. Lambda FLC tends to form dimeric and oligomeric complexes, which may interfere with accurate measurements
- While all three tests were shown to have benefits and drawbacks, this study showed that the three FLC assays should not be used interchangeably when determining patient treatment plan and response
- This study was based on analysis from a single-center study with a limited number of patients, and further clinical studies are needed to confirm these thresholds in larger cohorts