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Moreau C, Autier B, Cavey T, Rouger E, Norwood J, Bendavid C, et al. Evaluation of the Impact of Renal Failure on Correlation and Concordance between 2 Free Light Chain Assays. Clin Lymphoma Myeloma Leuk 2016.

Freelite and N Latex FLC analysis was performed on 1215 serum samples from patients with or without monoclonal gammopathy (MG+ or MG-).

  • There is no definition of how MG is defined in the methods section.
  • 876/1215 samples were from patients with MG (368 patients).
  • 818/1215 samples had renal function data available (455 patients).

Freelite and N Latex FLC results were compared for all 1215 samples.

  • There was a good correlation for κ and λ assays (Pearson’s correlation: κ: R=0.952, λ: R=0.930).
  • However, the assays are not equivalent (Pearson’s κ: r2=0.906, λ: r2=0.866).
  • Passing-Bablok regression for the κ and λ assays demonstrated that the bias between the two assays was neither constant nor-proportional.
    • N Latex FLC results tended to be higher at low FLC concentrations.
    • Freelite results tended to be higher at high FLC concentrations.

The 818 samples were grouped according to their renal function (eGFR, ≥60, 31-60, 15-30, <15 mL/min/1.73m2):

  • A good correlation was observed between Freelite and N Latex FLC κ and λ results irrespective of renal function (κ: R=0.926 – 0.974, λ: R=0.874 – 0.919).

The clinical interpretation of κ/λ FLC ratio for Freelite and N Latex FLC was compared.

  • 12.5% (102/818) of samples demonstrated discordant interpretations.

Patients were grouped according to their renal function and MG status (+/-).

  • Agreement increased as renal function decreased.
    • Concordance: eGFR≥60: 79.2%; 31-60: 88.8%; 15-30: 89.0%; <15: 92.4%.
    • Kappa coefficient: eGFR≥60: 0.63; 31-60: 0.80; 15-30: 0.81; <15: 0.88.

The FLC results of 41 patients with at least six consecutive samples were analysed

  • Note: The κ/λ FLC ratio is plotted on the monitoring graphs in the manuscript but dFLC/iFLC is recommended in the guidelines
  • 19/41 had a normal κ/λ FLC ratio for both assays during follow-up
  • 22/41 had an abnormal κ/λ FLC ratio during follow-up
    • 11/22 patients showed parallel results with both assays
    • 11/22 had discrepant result 
      • 4/11 were significant
        • 3/4 patients had a partial response (PR) with N Latex FLC but either no response or progressive disease (NR/PD) with Freelite
        • 1/4 patients had a PR with Freelite and NR/PD with N Latex FLC

 ‘We confirmed that quantitative discrepancies remain between the 2 assays and the methods are not interchangeable in the follow-up of MG.’

‘Interpretation must take into account clinical data and the same assay must be used for patient follow-up.’

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