Observations on the validation of immunochemical assays of monoclonal immunoglobulins

Assays of specific immunoglobulins by immunochemical methods are subject to a well-documented discrepancy when the test sample contains a monoclonal immunoglobulin of the class under assay. Demonstration of parallelism of the polyclonal standard and test sample log dose-response curves if proposed as an essential step in the validation of such assays, but theoretical considerations suggest that the mechanism underlying the observed discrepancy is unlikely to be associated with non-parallelism. The examination of 50 samples containing monoclonal immunoglobulins provides no evidence for rejecting the theoretical conclusions. It is shown here that demonstration of parallelism is of no value in establishing the validity of monoclonal immunoglobulin assays by immunochemical methods. The observation of relative changes in paraprotein concentration using an initial myeloma serum from the same subject as an arbitrary reference point is criticised.