Patients with chronic kidney disease (CKD) experience poorer outcomes compared with the general population. However, mortality attributable to a specific disease is often estimated from cause of death recordings, that may be incomplete or inaccurate. Relative survival is the ratio of patients’ observed survival to the general population expected survival, and reflects the excess of mortality due to the specific pathology without relying on cause of death. The estimated excess mortality can be modeled using multivariate flexible parametric survival analysis. While epidemiological findings based on relative survival are available for kidney transplant and dialysis data, evidence on mortality attributable to CKD is lacking.
Patients who entered the Prevention of Progressive Renal Insufficiency project (PIRP) between 2006 and 2011 were followed for at least one year until 2012 or death. The PIRP registry collects clinical data on CKD patients living in Emilia-Romagna Region who received an individualized pharmacological and dietary treatment aimed to reduce CKD progression. The study population included 2,179 patients with complete data. Patients were matched to the general population by calendar year, gender and age using regional ISTAT mortality tables.
Overall 7-years excess mortality in CKD patients was 28.8% (relative survival ratio=0.712). Subgroups with a low relative survival included patients with cardiovascular comorbidity, malnutrition, advanced CKD (stage 5) and with diabetic nephropathy. Factors significantly associated with higher excess mortality were age (over the background effect on mortality caught by matching mortality tables), CKD stage, being malnourished, previous cardiovascular events, diabetes, high phosphate levels, proteinuria and lower hemoglobin, while dialysis treatment was related to a lower excess mortality risk.
Our findings further underline that CKD patients are a particularly frail population, providing additional useful information for primary care physicians and nephrologists about factors to be monitored to decrease the risk of death from the onset of the disease onwards.
