This is the first study in Shanghai on surveillance of community CKD patients. However, before this study, little was known about the prevalence, disease awareness and its risk factors leading to the development of CKD in Shanghai. Our primary objective is to examine the CKD prevalence in Shanghai, which has about 20 million inhabitants, the disease awareness and its potential risk factors that will lead to CKD in the public. Our secondary objective is to detect the earlier cases of the CKD and those populations at high risk of developing CKD. Our third objective is, of course, to determine the most appropriate management strategies to improve the prognosis of our CKD patient population in Shanghai and ultimately improve their quality of life.
The epidemiological screening of the population in Beijing, examining only those aged 40 and above, revealed a 9.4% prevalent rate of CKD [16
]. In this study, our studied subjects ranged from the age of 18 to 104 years and 10.3% of our studied subjects were <40 years old. After studying 2554 adult participants randomly, it is clear that the prevalence of community CKD in Shanghai is 11.8%, which is very similar to the recent survey in America [17
]. The prevalence of CKD in Australia, by testing albumin and serum creatinine, is 16% among those aged 25 years and older [18
In our study, we used the staging of CKD recommended by KDOQI to categorize all the participants with kidney damage. However, it was proposed recently that stages 1 and 2 of CKD should be eliminated because they did not reflect the severity and complications of CKD accurately in elderly people [19
]. As the definition of CKD in elderly patients is controversial, further study is necessary to evaluate the staging of CKD in those populations.
In China, nephritis followed by diabetic nephropathy has been well documented as the second most leading cause of the CKD [3
]. Hence, the indicators that we used in this study to screen for the kidney damage evidence were albuminuria, haematuria and decreased kidney function.
Examining albuminuria in the routine analysis, in our view, is not only a relatively simple, non-invasive and cost effective measure to give the qualitative and quantitative assessment of the early stage of CKD, and to reveal those at high risk of developing CKD, but also is informative in the prediction of hypertension, diabetes and cardiovascular disease [20
]. We re-examined all our participants three months later if their baseline urinalysis was positive at screening. A total of 94.6% of those with albuminuria and 86.8% of those with haematuria or pyuria at the baseline screening undertook their repeated urinalysis. Results show that the prevalence of proteinuria is 1.2% in our study. In Singapore, the prevalence of proteinuria is 1.1% [5
]. In our study, the prevalence of albuminuria is 6.3% by the urinary albumin-to-creatinine ratio. In America [17
] and the Dutch PREVEND study, the prevalence of albuminuria is 9.3% and 7.2% by the urinary albumin-to-creatinine ratio, respectively. In Japan, it is 4.7% and 3.5% for males and females, respectively [22
]. Obviously, the urinary albumin-to-creatinine ratio could improve the detection rate and reduce the rate of misdiagnosis.
The K/DIGO guidelines also recommended examining the urinary albumin-to-creatinine ratio as the best index for the evidence of the early vascular endothelial injury [23
]. In our study, the prevalence of the urinary albumin-to-creatinine ratio is 6.3% compared to 7.2% reported in the PREVEND study [21
Our result shows that the prevalence of haematuria is 1.2% as compared with the 4.7% being reported in the AusDiab survey [18
]. The prevalence of pyuria in our study is 0.7%. We did exclude urinary infection or urinary stones in subjects with pyuria to avoid false positive interpretation.
Serum creatinine has been widely used to measure individual renal function but its assessment can be affected by age, gender, racial difference and GFR. Because our kidneys have a powerful compensatory function, serum creatinine will only begin to cripple up when our renal function has >50% deterioration. Hence, many stage 3 CKD patients do not necessarily have an abnormally high serum creatinine level. If the decreased kidney function is defined by the presence of the serum creatinine reaching 115 μmol/L, then we could only identify a 2.4% prevalence of the decreased kidney function in our study. We feel that measurement of the serum creatinine alone as the only criteria for the CKD diagnosis may be misleading. Hence, in this study, we detected the prevalent rate of decreased kidney function at 5.8% after using the simplified MDRD equation whereas 6.8% and 11.2% have been reported in the USA and Australia, respectively.
In our survey, it was shown that several clinical variables were associated with CKD. Those variables include hyperuricaemia, nephrolithiasis, anaemia, diabetes, central obesity, hypertension and age. Ageing has been described as a non-regulatory factor for the development of CKD [24
]. It has also been universally recognized to be in positive association with an arterial atherosclerotic change.
In recent years [25–27
], excessive abdominal fat (central obesity) has made more hazards to health than the fatty bottom and limbs. Now it is generally accepted that the waist circumference is the most simple and practical indicator to measure abdominal fat. The level of abdominal fat is an independent risk factor predictor of many diseases. It is more sensitive than the waist-to-hip ratio in estimating the abdominal fat. Our survey showed that elevated waist circumference is a risk factor for the development of CKD. Also, its prevalence is high at 14.4%. It is not related to general obesity, overweight and elevated waist-to-hip ratio. This is different from that observed in other countries [28
]. It may be that the cause is of ethnic origin. It also showed that central obesity is related not only to diabetes and cardiovascular disease but also to CKD.
The K/DOQI guidelines include the imaging examination in the definition of CKD. First we perform renal ultrasound examination in the epidemiological screening. In our study, the prevalence of renal cysts is 9.0%. At the same time, the prevalence of nephrolithiasis is higher in CKD patients (5.6%) than in non-CKD patients (1.7%). This is similar to the results being reported in America [29
]. Also in other studies, nephrolithiasis has been documented as a risk factor for the development of CKD [30,31
]. In 3.0% patients, ESRD was caused by nephrolithiasis. In China, the cause of nephrolithiasis is mainly due to dietary intake [32
]. The formation of calculus will be reduced by adjusting the diet structure. Then reducing prevalence of nephrolithiasis might be helpful to reduce prevalence of CKD. We first concentrate on the nephrolithiasis in the epidemiological screening. It will be further observed in the subsequent study. As the renal ultrasound examination is simple, non-invasive and of low cost, we think that it could be applied to the epidemiological screen of CKD to scree for nephrolithiasis.
In our study, hyperuricaemia is associated with CKD. In the studies published elsewhere, hyperuricaemia was reported to be a risk factor for the development of CKD and elevated levels of uric acid independently increase the risk for new-onset kidney disease [33–35
]. As CKD could cause elevated levels of uric acid while hyperuricaemia could also contribute to the progression of CKD, the predictive value of hyperuricaemia in CKD needs further study. Earlier management of the anaemia has been documented to retard the development of CKD [36
]. Our study shows that anaemia is another variable associated with CKD.
Some studies suggest that it is more cost-effective to screen among the high-risk population than among the general population [33
]. However, we find that the risk factor of CKD among the Chinese population is different from that in the USA and Europe. Maybe it is related to the spectrum of disease, race, diet and living habits. Therefore, we could not simply assume the risk factors of CKD among the US people to be the same as among the Chinese population. It is necessary to screen among the general population in China.
The awareness of CKD in the US is low [37
]. In our study, many patients with CKD have fewer clinical symptoms, which perhaps helps to explain why the disease awareness of CKD is low in spite of high prevalence rates, but this could be tested by regular laboratory examination. Even if we already have a simple test to detect the early stage of CKD, it has not been widely used clinically. Even if the participants had a health examination, half of them did not have a regular urine test. The awareness of CKD is increased with the decline in renal function, the development of CKD, complicated by hypertension, diabetes and cardiovascular disease.
In conclusion, the prevalence of CKD is 11.8% among the community population in Shanghai. It is 2.4%, 3.6%, 5.5%, 0.3% and 0.04% in stages 1–5, respectively. As it is more prevalent in the early stage of CKD in America, we should concentrate on the early stages of CKD in epidemiological survey and young people. Also the population shows decreased kidney function by the MDRD equation with a normal urine test. The screening was effective in identifying the CKD population and high-risk CKD population.