Serum free light chain assay (SFLCA)
Although measurement of Bence Jones protein is still used in some hospitals, NICE guidance recommends measuring serum free light chains (sFLC) via a serum free light chain assay. This is a much more sensitive technique and is particularly useful in diagnosing and monitoring light chain myeloma and certain types of non-secretory myeloma.
Healthy individuals have low levels of both kappa and lamda light chains:
- Kappa free light chains: 3.3 – 19.4 mg/L
- Lambda free light chains: 5.7 – 26.3 mg/L
- Kappa/lambda ratio: 0.26 – 1.65
In myeloma, the amount of one particular type of light chain is raised. This is often referred to as the “involved” light chain and the ratio becomes abnormal. A significantly abnormal ratio is often quoted as <0.1 or >7 and should initiate an urgent suspected cancer referral. It is important to remember however that an abnormal free light chain level may also result from other plasma cell disorders so other tests are needed to make a differential diagnosis.
It should be noted that some UK laboratories are starting to adopt new wider reference ranges in line with results of the Icelandic iStopMM study.