FLC refers to free light chains. For some of us they are Kappa, for others Lambda. The somewhat Y shapes normal cells are missing one leg for kappa, and the other for lambda, making the cell more L shapes. FLC plasma cells are like a guest that won't leave, they serve no purpose other than getting on our nerves (neuropathy) or bothering other cells. The healthy plasma cells at least go after invading organisms.

FLC is free light chains (kappa and lambda). Measurement of these is used to help diagnoses and also monitor multiple myeloma and amyloidosis. Usually, the ratio of these two chains is also calculated.