[Difficulties with immunofixation interpretation]

Immunofixation is widely used for monoclonal gammapathies identification and Bence Jones proteinuria research. In more of cases, interpretation is easy, but some difficulties persist. Five examples are presented and their causes are analysed; in our first case, seric immunofixation shows the problem generated by additives. These components are added to optimize antigen- antibody reaction but they can induce interferences; three cases of urinary immunofixation showing Bence Jones proteinuria with/or without complete monoclonal immunoglobulin are presented. The variability of immunsera avidity is sometimes a problem; a case of light chain disease associated with monoclonal IgA illustrate difficulties of interpretation when precipitin bands have nearly the same migration. These examples underline the great importance of regular controls of immunologic reagents. The use of two antisera with the same specificity but different origin is recommended in order to resolve difficulties with interpretation of immunofixation.