B2M and chronic kidney disease: Using the 2021 CKD-EPI creatinine equation (eGFRcr), ROC analysis showed that the area under the curve (AUC) for serum creatinine [AUC = 0.977 (95% CI: 0.882–0.999)] was comparable to that of serum cystatin C (p = 0.1035) [AUC = 0.908 (95% CI: 0.784–0.974)] and serum β2M (p = 0.1003) [AUC = 0.901 (95% CI: 0.775–0.970)] (Figure 2A).