For each sample, both κ and λ sFLCs should always be measured, and the κ/λ sFLC ratio calculated. Some centres (especially those taking part in clinical trials) may also wish to calculate the difference (dFLC) between the involved (iFLC) and uninvolved (uFLC) sFLCs. Definitions of other common terms/abbreviations are summarised in Table 7.3.
|Term||Definition||Comment||For a κ FLC tumour|
|iFLC||Involved FLC||The FLC type that is produced by the tumour||κ|
|uFLC||Uninvolved FLC||The FLC type that is the alternate light chain type to the iFLC
(not to be confused with urine FLCs)
|κ/λ sFLC ratio||κ/λ||A ratio of the concentration of κ to λ sFLCs||κ/λ|
|dFLC||iFLC - uFLC||The difference in the concentration between the iFLC and uFLC||κ - λ|
|ΣFLC||Summated FLC||The sum of κ and λ sFLC concentrations, determined by two separate assays||κ + λ|
Table 7.3. Summary of FLC terminology.
International Myeloma Working Group (IMWG) guidelines for sFLC analysis in multiple myeloma (MM) and related disorders recommend that the κ/λ sFLC ratio is calculated as part of the standard investigative workup of patients with suspected multiple myeloma (Chapter 25) . The ratio is now included in IMWG criteria for the diagnosis of multiple myeloma: an involved/uninvolved Freelite sFLC ratio ≥100 is designated a biomarker of malignancy (Section 25.2.1), and it is also important when documenting a stringent complete response (Section 25.3.5).