The impact of renal function on the clinical performance of FLC measurement in AL amyloidosis

Background: The measurement of circulating free light chains (FLC) is of utmost importance in immunoglobulin light chain (AL) amyloidosis, being a fundamental part of the diagnostic workup, prognostic stratification and assessment of response to therapy. Renal failure is a common feature of AL amyloidosis and can considerably affect the concentration of FLC. Methods: We assessed the impact of renal failure on the clinical performance of the Freelite assay in 982 consecutive, newly diagnosed patients with AL amyloidosis, 822 with estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2, and 160 with eGFR <30 mL/min/1.73 m2. Results: The diagnostic sensitivity of the κ/λ FLC ratio was lower for λ amyloidogenic FLC in patients with renal failure (81% vs. 60%, p<0.001) and the FLC concentration had no independent prognostic significance in patients with severe renal dysfunction. However, FLC response to chemotherapy could still discriminate patients with better outcome. Conclusions: Renal failure is a relevant interference factor when using the Freelite assay for the identification of the amyloidogenic light chain and for prognostic assessment in patients with AL amyloidosis and renal failure.