High prevalence of chronic kidney disease in population-based patients diagnosed with type 2 diabetes in downtown Shanghai

Abstract

Objective

This study aimed to evaluate the prevalence of chronic kidney disease (CKD) and the risk factors associated with CKD among Chinese patients diagnosed with type 2 diabetes aged over 30 in downtown Shanghai and to assess the relationship between CKD and diabetic retinopathy (DR).

Methods

We investigated 1039 Chinese patients diagnosed with type 2 diabetes aged over 30 by randomized cluster sampling in downtown Shanghai, and 1009 patients in this study were analyzed based on data integrity. Body measurements including height, weight, waist circumference and hip circumference, resting blood pressure, fasting blood measures, and urinary albumin-to-creatinine ratio (ACR), as well as the digitally stored fundus images, were investigated. Glomerular filtration rate (GFR) was estimated using the Cockcroft–Gault equation. The prevalence of CKD was calculated, and the risk factors associated with CKD were evaluated using stepwise logistic regression. The relationship between CKD and DR was evaluated using Spearman correlation and the chi-square test.

Results

The following were the results found in this study: (a) The prevalence rate of CKD (Stages 1–5) was 63.9% in Chinese patients diagnosed with type 2 diabetes, 8.8% in those with CKD Stage 1, 22.3% in those with CKD Stage 2, and 32.8% in those with CKD Stages 3–5 (GFR<60 ml/min/1.73 m²). The prevalence of CKD increased with age. (b) CKD patients were older and had higher duration of diabetes, systolic blood pressure, urea nitrogen, uric acid, creatinine, and ACR of the first urine than those without CKD. (c) Male patients had a higher percentage of CKD Stages 3–5, and female patients had a higher percentage of CKD Stages 1–2. (d) CKD was significantly associated with duration of diabetes, older age, systolic blood pressure, and serum urea nitrogen based on logistic regression analysis. (e) Of the patients without CKD, 15.6% had DR, and of those with CKD, 27.6% had DR. The decrease in GFR was significantly correlated with DR after controlling for sex, age, and albuminuria staging.

Conclusion

The high prevalence of CKD observed in Chinese patients diagnosed with type 2 diabetes aged over 30 in downtown Shanghai was similar to that in Western patients, and the cause of CKD is likely to be any of the following: type 2 diabetes, IgA nephropathy, hypertension, or any combination of these. The screening program for GFR in type 2 diabetic patients should be performed even on those with normoalbuminuria. The decrease in GFR might predict the occurrence of DR among patients diagnosed with type 2 diabetes.

Introduction

The incidence and prevalence of kidney failure caused by diabetes are rising, and its outcome is poor. Diabetes has become the most common cause of end-stage renal disease (ESRD) in some developed countries (U.S. Renal Data System, 2005). In the United States, diabetic nephropathy (DN) accounts for about 40% of new cases of ESRD (Centers for Disease Control and Prevention, 2005). In China, the rapid rise of diabetes mellitus also predicts a future prominent role of this disease in managing progressive renal failure, although glomerulonephritis (GN) is still the most common cause of ESRD (Lin, 2003, Wang et al., 2005). The increased prevalence of ESRD has fueled a rising interest in the evaluation of kidney damage and renal function among diabetic patients.

The Kidney Disease Outcomes Quality Initiative (K/DOQI) of the National Kidney Foundation (NKF) defined chronic kidney disease (CKD) as either kidney damage or decreased glomerular filtration rate (GFR) for 3 months or more (Levey et al., 2003, National Kidney Foundation, 2002); hence, both kidney damage and kidney function could be estimated by understanding CKD. There are few epidemiological data regarding the prevalence of CKD among Chinese patients diagnosed with diabetes.

Kidney damage is defined as pathologic abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies. Persistently increased excretion of albumin is a sensitive marker for CKD due to diabetes, glomerular disease, and hypertension (NKF, 2002). Albumin-to-creatinine ratio (ACR) in a spot urine specimen has replaced protein excretion in a 24-h collection as the preferred method for measuring proteinuria (American Diabetes Association, 2004, Ginsberg et al., 1983, Nathan et al., 1987, Rodby et al., 1995, Schwab et al., 1987, Zelmanovitz et al., 1997). Many earlier studies focused on serum creatinine levels as a marker of renal function (Iseki et al., 1997, Jones et al., 1998, Levey et al., 1988); however, creatinine was prone to being influenced by muscle mass, diet, and the method of assay (Clase et al., 2002a, Clase et al., 2002b). More recently, GFR has been considered the best indicator of renal function (Levey et al., 2003, National Kidney Foundation, 2002). Measuring GFR is expensive and cumbersome, and various methods of calculating estimated GFR from serum creatinine concentration have been studied, including the Cockcroft–Gault equation (Cockcroft & Gault, 1976) and several equations derived from the Modification of Diet in Renal Disease (MDRD) study population (Levey et al., 1999). The use of GFR estimates based on serum creatinine has gained popularity in both research and clinical practice, although some authors doubted their usefulness in epidemiological research (Bostom et al., 2002, Lin et al., 2003, Manjunath et al., 2001). We used increased ACR in a spot urine specimen as the marker of kidney damage and applied Cockcroft–Gault equation for estimating GFR in our study.

DN as evidenced by albuminuria, elevated blood urea nitrogen, and elevated blood creatinine is an excellent predictor for the presence of diabetic retinopathy (DR). Moreover, diabetic patients with nephropathy and retinopathy had lower GFR than diabetic patients with nephropathy but without retinopathy (Parving, Mogensen, Thomas, Brenner, & Cooper, 2005). An increased decline in GFR was significantly associated with DR among patients with nephropathy (Rossing et al., 2004, Trevisan et al., 2002). However, the relationship between CKD and DR was less predictable among patients with diabetes.

Therefore, we set out to accomplish two goals in this study. We calculated the estimates of the prevalence of CKD as manifested by albuminuria and/or low GFR (<60 ml/min/1.73 m²) determined using the Cockcroft–Gault equation in Chinese patients diagnosed with type 2 diabetes aged over 30. We also evaluated the relationship between CKD and DR among this population.