Measuring Bence Jones proteins with antibodies against bound immunoglobulin light-chains: how reliable are the results?

Protein mass concentrations of nine individual urinary Bence Jones proteins were determined via protein dry weight and compared (i) to immuno-nephelometric measurements using two different antisera against bound light-chains and (ii) to total protein concentrations determined by trichloroacetic acid nephelometry and the Biuret method. In each case, these four measurements differed significantly from each other and from the expected value (as determined by protein dry weight). The extent and direction of deviation were different for each measurement and varied between cases, but similar patterns were observed in different samples from the same patient. Apparently, these measurements can not be quantitatively compared between different individual Bence Jones proteins, but can be interpreted in terms of disease activity and therapeutic success for each patient. Accordingly, the quantitative expression of Bence Jones proteins should be restricted to relative terms, e.g. "arbitrary units" or "serum light-chain equivalents". This avoids the (potentially incorrect) statement of protein mass concentrations.