CDKN1A and chronic kidney disease: ROC-analyses of urinary p21 revealed an AUC of 0.7663 for the detection of patients at a low or moderate CKD risk, while the AUC was 0.9270 for the detection of patients at a high or very high risk of CKD (Fig. 3g), corroborating that urinary p21 increases with the severity of kidney disease.