A comparison between high resolution serum protein electrophoresis and screening immunofixation for the detection of monoclonal gammopathies in serum.

Background: There are a variety of initial laboratory tests or combinations of tests that can be performed when a monoclonal gammopathy is suspected including serum protein electrophoresis (SPEP), urine protein electrophoresis (UPEP), serum immunofixation (IFE) and serum free light chain assays. Some groups have recently used simplified "screening" IFE methods for the detection of monoclonal gammopathies leveraging the greater sensitivity of IFE over SPEP alone to improve the detection of monoclonal gammopathies. These screening techniques have been predominantly evaluated against lower resolution agarose gel electrophoresis techniques.

Methods: In this study we evaluated the diagnostic performance of the combined κ and λ light chain screening immunofixation (CLIF) in comparison to serum protein electrophoresis on a high-resolution (Sebia Hydragel 15 HR) agarose gel system. Each gel was interpreted by three adjudicators. A total of 156 patient samples were analysed. Adjudicated diagnoses based on the screening techniques were compared against the results of high resolution serum protein electrophoresis and high resolution standard immunofixation performed during routine laboratory operation. Where standard immunofixation was not performed a combination of a review of medical records, serum free light chains, UPEP and bone marrow aspirate and trephine and subsequent standard immunofixation and protein electrophoresis results where available were used to confirm the absence of a monoclonal gammopathy.

Results: In this cohort a total of 65 (41%) patients had a paraprotein confirmed by standard immunofixation. HR SPEP had a sensitivity and specificity of 95% and 85%, respectively, while CLIF had a sensitivity and specificity of 88% and 97%, respectively.

Conclusions: Overall we found that high-resolution gel serum protein electrophoresis using a Sebia Hydragel 15 HR system was more sensitive than a screening immunofixation method (CLIF) for the detection of paraproteins in patient serum in this patient cohort. The drawback of the greater sensitivity of HR SPEP was a higher false positive rate requiring an increased utilisation of follow up immunofixation electrophoresis.