End-stage renal disease is a global epidemia with an estimated incidence of 7% per year and high morbidity-mortality rate. Early detection of chronic kidney disease (CKD) and intervention for CKD complication is important to retard renal progression. However, "traditional uremic toxin" or "small water-soluble molecules" are poorly correlated with the renal function, uremic symptoms and outcomes of CKD patients.

Putative protein-bound solute, p-cresol, is accumulated in ESRD patients receiving dialysis therapy. This uremic solute was associated with endothelial dysfunction, immune dysregulation and can predict outcome in hemodialysis patient. P-cresol inhibits endothelial cell proliferation and endothelial response to inflammatory cytokines. In vitro, p-cresol decreases leukocyte transendotherliar migratory function and inhibit production of phagocyte reactive species. Clinically, p-cresol plays a pathophysiological role in the uremic toxicity. High free serum level of p-cresol is associated with mortality in hemodialysis patients.

Information of p-cresol in CKD patients is not available. The investigators hypothesized p-cresol can be accumulated in early CKD and have a positive correlation with the morbidity- mortality of CKD patients.

Value of p-cresol in different stages of CRF is still unknown. Information of p-cresol in CKD patients is not available. The investigators hypothesized p-cresol can be accumulated in early CKD and have a positive correlation with the morbidity- mortality of CKD patients.

The principal aim of this prospective cohort study is to investigate the association between total serum levels of p-cresol and the glomerular filtration rate. The correlation of level of p-cresol and morbidity-mortality in CKD patients will be also evaluated.

To determine the relationship, patients of nephrology clinic with a diagnosis of CKD were enrolled in this prospective study and follow-up for 1-year period. The association between total and free serum levels of p-cresol and the glomerular filtration rate were evaluated in CKD patients. The p-cresol level was correlated with other many inflammatory markers (white blood cell counts, ferritin, hs-crp, leptin) and also with the hospitalization rate secondary to cardiovascular and infectious event. The renal outcome and all-cause mortality was assessed. Determination of this relationship can help to establish an accurate marker for early detection of CKD and also its prognostic role in CKD patients.

Inclusion Criteria:

• All CKD patients attended at out-patient department of nephrology were included for analysis.
• The inclusion criteria were adults aged > 18 y/o or < 80 y/o
• Estimated GFR or CCR < 60 ml/min
• No spontaneous renal improvement or progression in past 3 months.

Exclusion Criteria:

• Recent cardiovascular disease (Coronary artery disease, myocardial ischemia, cerebrovascular disease or peripheral artery disease) in past 3 months
• Recent infections requiring admission in past 3 months
• Uncontrolled hypertension
• Serum albumin level < 2.5mg/dL
• Unwilling to participate in the trial.

All CKD patients attended at out-patient department of nephrology were included for analysis. The inclusion criteria were adults aged > 18 y/o or < 80 y/o; estimated GFR or CCR < 60 ml/min; no spontaneous renal improvement or progression in past 3 months.