Discrepancy between FLC assays: only a problem of quantification?

Evaluation of the Impact of Renal Failure on Correlation and Concordance Between 2 Free Light Chain Assays

“…Nevertheless, few discrepancies remained between both tests and the reason for these differences is still unknown. We confirmed that quantitative discrepancies remain between the two assays and the methods are not interchangeable in the follow-up of monoclonal gammopathy 12,16,23 .…”

“…In 2011, another N Latex FLC method using monoclonal antibodies was developed by Siemens (Marburg, Germany) 9 . These two assays are not entirely equivalent and seem to have limited clinical utility in detecting monoclonal gammopathy in some clinical situations, and care should be taken for interpretation if assays are switched [10][11][12][13][14][15][16][17] .…”

“…consider a moderate renal insufficiency as the eGFR was 31-60 ml/min/1.73 m 2 (designated CKD 31-60 ), severe renal insufficiency as eGFR 15-30 ml/min/1.73 m 2 (designated CKD [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] ) and renal failure as eGFR less than 15 ml/min/1.73 m 2 (designated CKD <15 ).…”

“…This confirms that a monoclonal protein, depending on its biochemical/biophysical characteristics could present different stoichiometric interactions with different test antibodies 10 . This observation is usually related with the presence of FLC dimers (and sometimes multimers) in mismatching sera which present a probably modified reactivity with antibody detection and light diffraction properties 16,26 .…”

Protein electrophoresis and serum free light chains in the diagnosis and monitoring of plasma cell disorders: laboratory testing and current controversies

“…As a postscript to this issue, CCLM recently received an interesting Letter to the Editor about the quantitative FLC differences between Freelite and N Latex monoclonal λ FLC results [42]. Using gel chromatography and Western blotting, with and without disulfide bond reduction of the sample, the authors concluded that the Freelite assay may selectively recognize the dimeric λ FLC in a patient with MM whereas the N Latex assay appeared to recognize the monomeric form.…”