Is the absolute value of the FLC or the free κ/λ ratio more important?
Serum FLC abnormalities should be established by assessing both the concentrations of the clonal free light chain, the alternate free light chain and the free κ/λ ratio. This is optimally performed using a κ/λ log plot for each patient’s result which is then compared with normal range and disease group data. This elegantly identifies monoclonal FLC diseases from polyclonal FLC abnormalities and individuals in the normal range. Since renal function is frequently affected in myeloma patients, the alternate light chain concentrations are often elevated but the κ/λ ratio may still be highly abnormal. If the patient has bone marrow suppression, the individual FLC concentrations might be low, in which case the κ/λ ratio may be more helpful. This is typical of patients undergoing chemotherapy and in patients with nonsecretory myeloma and primary amyloidosis with bone marrow suppression. Clinical judgement should be used in these cases. If either the FLC concentrations or the κ/λ ratios are ou
