DKK1 and chronic kidney disease: On the basis of the ROC curve for differentiating CKD (Figure 1), a cutoff value of 641.8 pg/mL for plasma DKK-1 levels provided a sensitivity of 66.1% and specificity of 66.7% for differentiating CKD (area under the curve = 0.661; 95% CI: 0.593–0.729; p < 0.001).