Kinetics of Serum-Free Light Chain Removal by High-Cutoff Hemodialysis in Patients with Multiple Myeloma and Acute Renal Failure

<i>Background and objectives</i>: Cast nephropathy is the main cause of acute renal failure in patients with multiple myeloma. There are conflicting data on whether removal of serum free light chains (sFLCs) with a high-cutoff (HCO) dialyzer has a favorable effect on the recovery of renal function. This may in part be explained by differences in the efficacy of sFLC removal by HCO dialysis and treatment responses to anti-plasma cell therapy between studies. We studied the removal of sFLCs during HCO treatment in detail in relation to treatment response. <i>Materials and methods</i>: Pre-dialysis serum and dialysate levels of sFLCs were simultaneously and repeatedly measured during the first two HCO treatments in 10 patients with kappa (κ)- and 5 patients with lambda (λ)-producing myeloma that presented with dialysis-dependent renal failure at our institution between 2009 and 2024. <i>Results</i>: The average change in sFLCs during 6 h treatments was -57 ± 13%, but it varied widely between -29% and -77%. Mean reductions in sFLCs were comparable for κ and λ (-61.4 ± 19.1% and -55 ± 16.7%, respectively; <i>p</i> = 0.78). The average clearance of sFLCs at 15 min after the start of HCO dialysis was 42.1 ± 8.5 and 27.4 ± 15.6 mL/min for κ and λ, respectively (<i>p</i> < 0.01). Clearances decreased to 27.2 ± 11.3 for κ and 13.8 ± 7.9 mL/min for λ after 6 h of HCO treatment (<i>p</i> = 0.042). Renal function recovered in 11 patients (73%). In three of the four patients whose renal function did not recover, sFLC levels were >5 g/L at any time beyond 2 weeks after the start of HCO treatment. <i>Conclusions</i>: Although the clearance of κ was higher compared to λ, reductions in sFLCs were similar for κ and λ. We speculate that this discrepancy is explained by greater adherence of λ to the HCO membrane. Patients whose renal function did not recover had less of a reduction in sFLC levels during HCO treatment, probably due to a suboptimal hematological response to anti-plasma cell therapy.