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

<b><i>Introduction:</i></b> Multiple myeloma (MM) frequently involves the kidneys, resulting in acute, subacute, or chronic kidney disease (CKD). Patient- and treatment-related factors are associated with the long-term development of CKD. The aim of our study was to examine the association of serum free light chain (FLC) levels, measured at the time of diagnosis of MM, and CKD at subsequent follow-up. <b><i>Methods:</i></b> Patients with newly diagnosed MM were identified using cancer registries at five hospitals. The primary outcome was low eGFR (&lt;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. <b><i>Results:</i></b> A total of 149 patients met the inclusion criteria. Patients with an FLC level above the median had a higher frequency of hypertension (54% vs. 81%; <i>p</i> &lt; 0.001), hyperlipidemia (37% vs. 56%; <i>p</i> = 0.018), low eGFR at the time of diagnosis (43% vs. 66%; <i>p</i> = 0.006), and a higher MM stage (<i>p</i> = 0.018). On multivariable analyses, after adjustment for several covariates, serum FLC level (per each 100 mg/L) was independently associated with low eGFR or dialysis dependence at follow-up (adjusted odds ratio [aOR] 1.021; 95% CI: 1.002, 1.041; <i>p</i> = 0.033). This association persisted for the composite outcome of low eGFR, dialysis dependence, or death (aOR 1.034; 95% CI: 1.006, 1.063; <i>p</i> = 0.018). <b><i>Discussion/Conclusion:</i></b> Higher serum FLC level measured at the time of MM diagnosis is independently associated with CKD at up to 12 months of follow-up.