The RRI was negatively correlated with the CD34 PPA-glomerulus (Figure 9), positively correlated with age, and was not correlated with the CD34 PPA-total, CD34 PPA-peritubular capillary, or Masson PPA (total, glomerulus, or peritubular capillary) with disease progression from CKD stages 2 to 5. Here, CD34 is linked to chronic kidney disease.