Serum free light chain assay reduces the need for serum and urine immunofixation electrophoresis in the evaluation of monoclonal gammopathy

This version was published on 1 September 2009

Ann Clin Biochem 2009;46:407-412
doi:10.1258/acb.2009.009038
© 2009 Association for Clinical Biochemistry

 

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Original Articles


Richard B Fulton1 and
Suran L Fernando1,2,3


1 PaLMS Immunorheumatology Laboratory;
2 Department of Clinical Immunology, Royal North Shore Hospital;
3 Northern Clinical School, University of Sydney, Sydney, Australia


Corresponding author: Richard Fulton, PaLMS Immunorheumatology Laboratory, Royal North Shore Hospital, Reserve Road, St Leonards 2065, Sydney, Australia. Email: rfulton{at}nsccahs.health.nsw.gov.au


Background: The potential for serum free light chain (sFLC) assay measurementsto replace urine electrophoresis (uEPG) and to also diminishthe need for serum immunofixation (sIFE) in the screening formonoclonal gammopathy was assessed. A testing algorithm formonoclonal protein was developed based on our data and costanalysis.

Methods: Data from 890 consecutive sFLC requests were retrospectivelyanalysed. These included 549 samples for serum electrophoresis(sEPG), 447 for sIFE, and 318 for uEPG and urine immunofixation(uIFE). A total of 219 samples had sFLC, sEPG, sIFE and uEPG+ uIFE performed. The ability of different test combinationsto detect the presence of monoclonal proteins was compared.

Results: The sFLC / ratio (FLC ratio) indicated monoclonal light chainsin 12% more samples than uEPG + uIFE. The combination of sEPGand FLC ratio detected monoclonal proteins in 49% more samplesthan the combination of sEPG and sIFE. Furthermore, the sEPG+ FLC ratio combination detected monoclonal protein in 6% moresamples than were detected by the combined performance of sEPG,sIFE, uEPG and uIFE. However, non-linearity of the assay, theexpense of repeat determinations due to the narrow measuringranges, and frequent antigen excess checks were found to belimitations of the sFLC assay in this study.

Conclusion: The FLC ratio is a more sensitive method than uIFE in the detectionof monoclonal light chains and may substantially reduce theneed for onerous 24 h urine collections. Our proposed algorithmfor the evaluation of monoclonal gammopathy incorporates thesFLC assay, resulting in a reduction in the performance of labourintensive sIFE and uEPG + uIFE while still increasing the detectionof monoclonal proteins.

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