Prevalence of impaired renal function in the elderly in the St. Petersburg District: results of the Crystal study.

Chronic kidney disease (CKD) has a high prevalence in the elderly. It has been recognized as an independent cardiovascular risk factor and detecting CKD is also important to ensure the appropriate dose of medication and to prevent further damage by limiting the use of potential harmful drugs. The aim of the research was to study the prevalence of CKD in elderly (> or = 65 years) in a St. Petersburg district and to study the impact of using different methods to estimate the GFR on the prevalence of different stages of CKD. The cross-sectional analysis of prospective population based study in the district of Kolpino was conducted. All creatinine measurements were performed in the same laboratory. Renal function was assessed calculating the eGFR using different creatinine based formulas. 611 elderly (65-91 years) were examined. Using the MDRD formula a prevalence of CKD stage III-V for males of 11% was found in stratum 1 and of 15% in stratum 2 and for females prevalence was 14 and 29%, respectively. A considerable mismatch in classification of stages of CKD was found when comparing the MDRD based estimations with the CG-based ones. Compared to what has been reported internationally in other studies a considerable lower prevalence of CKD stage IV-V was found in both age groups. Thus, the prevalence of an impaired renal function in elderly in the St. Petersburg district is relatively low, especially in the subgroup of males aged 75 years and over compared to what been reported in other studies. The CG and MDRD formula generate significantly different results when they are used to classify the population of elderly according to the stages of CKD.