| Background:The proportion of the elderly population is increasing gradually, in accompany with a simultaneously increasing awareness of age-related changes in renal function. Glomerular filtration rate (GFR) as an indicator of renal function, measured or estimated, has been used in the assessment of renal function for the past many years. A number of studies have shown kidney function falls markedly with increasing age among adults after the age of40years, and that the rate of decline in GFR approximates1ml/min per year. Rowe et al. reported a10-year analysis of the first longitudinal study with data on within-individual changes in renal function over time. In this report, cross-sectional analysis provided results similar to those observed in previous studies. The intra-individual changes in creatinine clearance over time showed the decline similar to the cross-sectional results suggesting that there did not appear to be any significant effect of selective mortality or of differences among cohorts in the cross-sectional results. A subsequent study confirmed these findings but showed that one third of the subjects had no absolute decrease in renal function, which was composed by254normal subjects followed between1958and1981from the Baltimore Longitudinal Study of Aging. However, studies with data on intra-individual changes in kidney function over time are still limited now. Furthermore, information on factors which converge on a road towards decline in kidney function is so rare in the healthy population. It is worthy to be further investigated whether or not factors affecting the decline in GFR in the healthy population are the same as those with chronic kidney disease (CKD). Especially, results of an association between the decline in renal function with age and atherosclerosis are controversial. In conclusion, the purpose of our research is described as follows:①changes in renal function with age in a Chinese healthy population;②predictors of the progression of renal function with ageing in healthy individuals;③association of age-related decline in renal function with the outcome of carotid plaque in healthy adults. Thus, we provide a theoretical basis for the clinical interventions of physiological decline of renal function in the elderly.Methods:It was a community-based cross-sectional and longitudinal study, which was conducted in Beijing from10communities in July2003and December2008. By a random cluster sampling method, a total of301healthy volunteers (140men and161women) between the age29and96(60±12years) in the baseline survey, participated in this study. They were selected finally after series of questionnaires, physical examination, blood pressure measurement, conventional blood and urine parameters, biochemical blood parameters and carotid ultrasound scanning. After5years of follow-up, we repeated all measurements of the target population mentioned above and265subjects were enrolled in the second survey, of whom20individuals had incomplete information, leaving a group of245individuals having complete information. The follow-up rate was81%. The estimated GFR (eGFR, ml/min/1.73m2) was calculated using the new estimating equation (Chronic Kidney Disease Epidemiology Collaboration, CKD-EPI). We calculated the rate of change of all clinical parameters over five years, e.g. the formula for determining the annual rate of change (%) in eGFR is as follows:△eGFR=[(later-baseline)/baseline]×100%. The rise (or fall) in eGFR was defined by△eGFR/5value greater than or equal to1%(or less than or equal to-1%). Thus, changes in eGFR during follow-up was then divided into three groups, i.e. rise (≥1%per year, N=35), no change (greater than-1%and less than1%per year, N=72), and fall (≤-1%per year, N=138). At entry, subjects were assigned into four different age groups by15-year age groups, i.e. young (<44years, N=39), middle age (45～59years, N=86), old (60～74years, N=98) and very old (≥75years, N=22). The group mean ages±SD were:40±4years,52±4years,68±4years and79±3years, respectively. Changes in presence of carotid artery plaques between 2003and2008were further categorized into four groups, i.e. Group1(without plaque in two occasions, N=129), Group2(with nascent plaque at follow-up, N=36), Group3(with plaque regression at follow-up, N=29) and Group4(with plaque in two occasions, N=51). Clinical parameters were compared among different groups to analyze the values of eGFR, changes in eGFR with age, prevalence of age-related decline in eGFR, effecting factors of renal function and association of the age-related decline in eGFR with carotid plaque.Results:①Cross-sectional analysis of baseline and follow-up data by15-year age groups showed a progressive linear decline in both baseline eGFR from117ml/min/1.73m2at age40to80at age79and follow-up eGFR from111at age45to70at age84. It can be clearly seen that the mean annual rate of decline in both baseline eGFR (0.9ml/min/1.73m2) and follow-up eGFR (1.1ml/min/1.73m2) approximates1ml/min/1.73m2/year.②During5years of follow-up, eGFR decreased from98.1±15.6to90.4±17.3ml/min/1.73m2.14%of individuals experienced a rise in eGFR,29%no change and57%a fall.③Analysis of multiple linear regression was used to screen main factors predicting a faster decline in eGFR, and results showed that five baseline factors-older age, higher low-density lipoprotein cholesterol(LDL-C), higher eGFR, higher systolic blood pressure(SBP) and lower serum transferrin(TRF)-Were identified as significant (P<0.05) baseline predictors of eGFR decline.④The difference in mean eGFR value between the presence and absence of plaque groups was analyzed by the Student’s t-test. The mean eGFR value in the presence of plaque group was significantly lower than that in the absence of plaque group,92.6±15.4vs101.7±14.8ml/min/1.73m2(P<0.001) at baseline and79.7±15.8vs96.3±15.2ml/min/1.73m2(P<0.001) at follow-up.⑤Results of t-test showed that in individuals without carotid plaque at baseline (Group1, Group2), there was no significant difference between mean initial eGFR value in Group1and Group2with a P value of0.135, but that a significant difference existed between mean follow-up eGFR value in Group1and Group2(P<0.001). Likewise, in individuals with plaque at baseline (Group3and Group4), the mean follow-up eGFR value in Group3was significantly higher as compared to that of Group4(P=0.001) and there was still no difference between baseline eGFR in Group3and Group4with a P value of0.482.⑥The distribution of percent decrease of eGFR per5years based on four plaque groups, which was analyzed by one-way ANOVA. The mean△eGFR values in the two groups with carotid plaque at the end of the study (Group2, Group4) were significantly higher than the two groups without plaque (Group1, Group3), P<0.001.⑦Comparison of mean△eGFR value among various plaque groups in both sexes used by analysis of covariance with correction for age and baseline eGFR. There was still a significant difference in△eGFR value among four plaque groups in both males and females, P=0.001vs P=0.002.⑧With correction for age and gender, multiple logistic regression analysis was used to analyze the impact of different years, different groups of individuals (with or without plaque at entry) on changes in eGFR over time. The presence of carotid plaque (OR=2.6,95%CI1.6to3.9, P<0.001) was included in the final model as a significant and independent factor affecting a greater variability in the rate of change in eGFR.Conclusion:Cross-sectional analysis confirms the conclusion that renal function declines with increasing age. However,43%of participants did not experience a decline in eGFR during follow-up. Besides older age and higher initial eGFR, presence of atherosclerotic carotid plaque, higher SBP, higher LDL-C and lower TRF are independent risk factors predicting for a more rapid decline of renal function in the healthy Chinese population. |
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