**3.1 Patient-related factors**

Decline of RRF is an unavoidable phenomenon caused by the degenerative and fibrosis process of chronic kidney disease (CKD). However, the rate of RRF loss is different among patients and may be affected by other factors such as patient-related factors, treatment modalities and practice patterns (Jansen, Hart et al, 2002). Patient-related factors include age, causal nephropathy and comorbid conditions. Decline of RRF has been shown to be age dependent (Hung, Young, 2003). Intercurrent events such as recurrent blood pressure drop during HD, cardiac events and sepsis may precipitate loss of RRF. Diabetics on PD have been shown to have a more rapid decline in RRF than nondiabetics (Singhal, Bhaskaran et al, 2000). Comorbid conditions, including congestive heart failure, poorly controlled hypertension, and coronary artery disease, also are associated with faster rates of RRF decrease (Shin, Noh et al, 1999). Patients with CKD secondary to glomerular disease lose RRF more rapidly than those with tubulointerstitial disease (Iest, Vanholder et al, 1989). In a large multicenter study, the majority of patients with adult polycystic kidney disease were found to maintain a GFR greater than 2 ml/min for more than 4 years (Van Stone, 1995). Patients returning to dialysis therapy after kidney transplant failure have a more rapid decline in RRF than those initiating dialysis therapy with native kidney disease (Davies, 2001).
