Cystatin C as Biomarker for the Evaluation of Renal Outcome in <scp>AL</scp> Amyloidosis

Cystatin C (CysC) has emerged as a novel and potentially more reliable biomarker for the estimation of glomerular filtration in the general population in patients with various conditions. In AL amyloidosis, the current renal staging system and renal response criteria are based on proteinuria and creatinine-based eGFR. We explored the prognostic role of CysC and of estimation of eGFR based on CysC-based equations in a cohort of 195 patients with newly diagnosed AL amyloidosis with renal involvement. Baseline CysC level was strongly and independently associated with progression to dialysis, and CysC levels ≥ 1.9 mg/L can be used in combination with the current renal staging system to identify patients with different risk of progression to dialysis among renal stages 2 and 3. eGFR based on CysC performed at least similarly to eGFR based on creatinine alone (by CKD-EPI race free formula) and the cutoff of 30 mL/min/1.73 m² could better predict progression to dialysis at 2 years. At 6 months landmark, an increase in CysC by ≥ 1 mg/L was associated with higher risk of progression to dialysis (HR: 19.8, 95% CI 6.5-60.5, p < 0.001); a reduction of CysC based eGFR ≥ 30% was also associated with poor renal outcome, with a prognostic performance similar to current renal progression criteria. In conclusion, CysC provides prognostic information regarding the renal outcomes in patients with AL amyloidosis independently of the established biomarkers, but requires further validation.