[Standardization of immunofixation technique for the detection and identification of serum paraproteins].

Diagnosis and follow up of paraproteinaemias require identification and typing of paraproteins. Immunoelectrophoresis is the most commonly used method, though a lengthy one and with low sensitivity. Immunofixation is more sensitive, faster and of easier interpretation, specially when monoclonal proteins are present in low concentration in the serum and/or urine. Immunofixation includes two steps. The first is electrophoresis; the second is immunofixation of the separated antigen by use of antiserum. The latter step is accomplished by layering the antiserum over the agarose gel immediately after electrophoretic separation of the proteins resulting in antigen/antibody precipitation. PURPOSE--The objective of this study is to standardize the technique of immunofixation and compare it to immunoelectrophoresis. METHOD--The serum of 28 patients (25 with multiple myeloma and 3 with polyclonal hypergammaglobulinaemia) was analysed and compared to 6 normal subjects. All were submitted to electrophoresis on agarose gel, immunoelectrophoresis and immunofixation. RESULTS--Dilution of the serum to produce a concentration suitable for immunofixation is critical. In our study the correct paraprotein concentration was 28 to 35 g/dl. Both methods detected and identified the paraprotein in 21 (84%) of the samples and in 2 (8%) it was not detected at all. In two of the samples, only immunofixation was able to detect and identify the paraprotein. There was not any monoclonal band observed either through the electrophoresis or immunoelectrophoresis that was not detected by the immunofixation. CONCLUSION--These results show that immunofixation is more sensitive than immunoelectrophoresis and therefore should be incorporated into diagnosis routine.