Association of Serum Free Light Chain Level with Long Term Kidney Function in Patients with Newly Diagnosed Multiple Myeloma

Introduction: Multiple myeloma frequently involves the kidneys, resulting in acute, subacute, or chronic kidney disease. Patient- and treatment-related factors are associated with the long-term development of chronic kidney disease. The aim of our study was to examine the association of serum free light chain (FLC) levels, measured at the time of diagnosis of multiple myeloma, and chronic kidney disease at subsequent follow-up.

Methods: Patients with newly diagnosed multiple myeloma were identified using cancer registries at five hospitals within an integrated healthcare system. Patients without an initial serum FLC level and a baseline and follow-up eGFR were excluded. The primary outcome of interest was an eGFR <60 mL/min/1.73 m2 or dialysis dependence, and a secondary composite outcome of low eGFR, dialysis dependence, or death at the last follow-up, up to 12 months from diagnosis. Logistic regression analyses were performed to examine the association of serum FLC level with the outcomes of interest, after adjustment for several covariates.

Results: A total of 300 patients were identified and 149 patients (50%) met the inclusion criteria. The median serum FLC level was 634 mg/L. Patients with a median FLC level above the median had a higher frequency of hypertension (54% vs. 81%; P < 0.001) and hyperlipidemia (37% vs. 56%; P = 0.018) and were more likely to have a low eGFR at the time of diagnosis (43% vs. 66%; P=0.006) and a higher multiple myeloma stage of disease (P=0.018). On multivariable analyses, after adjustment for age, hypertension, chronic kidney disease, FLC subtype, and multiple myeloma stage, serum FLC level (per each 100 mg/L) was independently associated with higher odds for low eGFR or dialysis dependence at follow-up (adjusted odds ratio [OR] 1.021; 95% CI 1.002, 1.041; P=0.033). This association persisted for the composite outcome of low eGFR, dialysis dependence, or death (adjusted OR 1.034; 95% CI 1.006, 1.063; P=0.018).

Discussion/conclusion: Higher serum FLC level measured at the time of multiple myeloma diagnosis is independently associated with chronic kidney disease at up to 12 months of follow-up. Additional studies are required to validate these findings.