The antigen used for production of this antibody is polyclonal free kappa-chains prepared from pooled normal human immunoglobulin. The specificity is directed against the hidden determinants of the kappa-chain, thus, this antibody reacts with free kappa-chains (monoclonal as well as polyclonal), but not with the kappa-chains in intact immunoglobulin molecules.
It is useful for screening unconcentrated urine samples for the presence of free kappa-chains. However, it is important to note that a negative reaction does not prove the absence of free kappa-chains as these proteins from some patients do not precipitate with this antibody possibly because they do not expose free light chain determinants. A positive reaction must not be considered as definite proof of the presence of monoclonal free kappa-chains, but should rather lead to further investigation by immunofixation or immunoelectrophoresis in order to establish the monoclonal nature of the reacting kappa-chain. This is necessary because polyclonal light chain excretion is not uncommon in proteinuria of various types. Concentrated urine samples from normal subjects may also contain detectable levels of polyclonal free light chains.
For gel precipitation techniques like double immunodiffusion, immunoelectrophoresis and immunofixation, it is useful to incorporate 4% freshly prepared polyethylene glycol, MW 6000, in the agarose gel to improve the sensitivity of free light chain detection.