Quantitation of free kappa light chains in serum and urine using a monoclonal antibody based inhibition enzyme-linked immunoassay.

The murine monoclonal antibody K-1-21 with specificity for free but not heavy chain-associated kappa chains was used to develop an inhibition enzyme immunoassay for quantitation of free kappa chains in serum and urine. The assay utilizes a biotin conjugate of the monoclonal antibody and has an effective working concentration range of 0.5-50 micrograms/ml free kappa chain. Normal serum and urine yielded mean values of 1.2 and 4.9 micrograms/ml respectively using this assay system. Serum levels in patients with kappa chain myelomatosis ranged from 2 to 1700 micrograms/ml while serum from patients with lambda chain malignancies exhibited normal free kappa chain levels. The importance of the ability to readily quantitate light chains in serum was demonstrated by the finding in one patient of an absence of free kappa chains in the urine despite elevated levels of serum kappa chains. A significant drop in serum-free kappa chain levels was observed in this patient following a course of chemotherapy. The assay should prove valuable in the diagnosis, prognosis and monitoring of B cell neoplasias characterized by free kappa light chain secretion.