The antigen used for production of A0101 is a pool of human free lambda-chains. The specificity is directed against the hidden determinants of the lambda-chain, thus, A0101 reacts with free lambda-chains (monoclonal as well as polyclonal), but not with the lambda-chains in intact immunoglobulin molecules.

A0101 is useful for screening unconcentrated urine samples for the presence of free lambda-chains. However, it is important to note that a negative reaction does not prove the absence of free lambda-chains as these proteins from some patients do not precipitate with A0101, possibly because they do not expose free light chain determinants. A positive reaction with A0101 must not be considered as definite proof of the presence of monoclonal free lambda-chains, but should rather lead to further investigation by immunofixation or immunoelectrophoresis in order to establish the monoclonal nature of the reacting lambda-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.