Kidney Disease in Diabetes

Excerpt

Persons with diabetes make up the fastest growing group of kidney dialysis and transplant recipients in the United States. In 1985, when the first edition of Diabetes in America was published, 20,961 persons with diabetes were receiving renal replacement therapy, representing 29% of all new cases of end-stage renal disease (ESRD). By 2012, 239,837 persons with diabetes were on renal replacement therapy, accounting for 44% of all new ESRD cases. The increased count reflects growth in diabetes prevalence and increased access to dialysis and transplantation. Those with a primary diagnosis of diabetes have lower survival relative to other causes of ESRD, primarily because of the coexistent morbidity associated with diabetes, particularly cardiovascular diseases (CVD). While survival on dialysis has slowly improved across modalities since the 1990s, it remains reduced in persons with diabetes, half of whom die within 3 years of beginning dialysis in the United States. Similar to persons with ESRD in general, the leading causes of death among adults with diabetes who started dialysis in 1995–2009 were CVD (58% of the deaths) and infections (13% of the deaths). Kidney transplant recipients with diabetes have much better survival than those on dialysis, indicating a significant impact of the type of renal replacement therapy (transplant versus dialysis) on long-term survival.

Kidney failure affects about 1% of persons with diabetes in the United States. A considerably higher proportion, about 40%, have less severe kidney disease. Since the second edition of Diabetes in America was published in 1995, a wealth of new information has contributed substantially to the understanding of kidney disease associated with diabetes. In 2002, the National Kidney Foundation’s Kidney Disease Outcome Quality Initiative published a uniform definition of chronic kidney disease (CKD) and classification of its stages irrespective of underlying cause, thus providing a common language for defining both the severity and prognosis of kidney disease. The definition and classification of CKD were subsequently updated and refined by the Kidney Disease: Improving Global Outcomes in 2012. Accordingly, CKD is classified based on both albuminuria and glomerular filtration rate (GFR) categories, and together with kidney failure, these conditions are collectively referred to as CKD, regardless of etiology. In addition, the Kidney Disease: Improving Global Outcomes recommends using equations to estimate GFR (eGFR), which include the routinely obtained variables serum creatinine, age, sex, and race/ethnicity. The use of serum cystatin C, an endogenous filtration marker less influenced than serum creatinine by variations in muscle mass, diet, and tubular secretion, has emerged as an alternative or an adjunct to serum creatinine-based equations, particularly in persons with diabetes, in whom early kidney disease is often characterized by elevated GFR.

Since the late 1990s, new molecular mechanisms have been defined that are helping to explain the development and progression of diabetic kidney disease. Glomerular structural lesions were found to explain 95% of the variability in albumin excretion and 78% of GFR variability. The latter percentage increased to 92% by adding indices of glomerular-tubular junction abnormalities and interstitial expansion to the regression models. Podocyte injury appears to play an essential role in the progression of diabetic nephropathy. In persons with either type 1 or type 2 diabetes, podocyte changes may occur even before the increase in albuminuria, suggesting that diabetes itself may induce podocyte alterations.

Much has also been written about the prognostic implications of CKD. Elevated albuminuria and low GFR are associated with ESRD, fatal and nonfatal CVD, and all-cause mortality. A meta-analysis of 1,024,977 participants (nearly 13% with diabetes) from 30 general population and high-risk cardiovascular cohorts and 13 CKD cohorts indicated that while the absolute risks for all-cause and CVD mortality are higher in the presence of diabetes, the relative risks of ESRD or death by eGFR and albuminuria are similar with or without diabetes. These findings underscore the importance of kidney disease per se as a predictor of important clinical outcomes, regardless of the underlying cause of kidney disease. New biomarkers of diabetic kidney disease appear to have additional prognostic information beyond that provided by albuminuria. These markers include kidney injury molecule 1, liver fatty acid-binding protein, N-acetyl-β-D-glucosaminidase, neutrophil gelatinase-associated lipocalin, β-trace protein, β₂-microglobulin, and tumor necrosis factor receptors 1 and 2.

Many concepts about risk factors for CKD illustrated in this chapter have not changed since 1995, and where they have, those changes are discussed. In particular, major advances have been made in elucidating the genetic and epigenetic complexity of CKD, which contributed to defining cellular metabolic memory and the understanding of the longlasting effects of strict glycemic control observed in persons with type 1 diabetes or type 2 diabetes.

Improvements in the management of persons with diabetes and CKD have extended the time course from onset of severe albuminuria to ESRD and reduced the occurrence of CVD. In type 1 diabetes, the combined Diabetes Control and Complications Trial (DCCT) and its long-term follow-up, the Epidemiology of Diabetes Interventions and Complications (EDIC) observational study, indicated that intensive early metabolic control reduced the risk of impaired GFR by 50% and of CVD outcomes by 42%, with a specific 57% decrease in myocardial infarction, stroke, or death from CVD, effects that were partly mediated by the reduced incidence of diabetic kidney disease. Among persons with type 2 diabetes, a meta-analysis of randomized controlled trials indicated that more intensive glycemic control (glycosylated hemoglobin [A1c] <7%) was associated with a significant 10% reduction in albuminuria but had no effects on mortality, kidney failure, or other vascular outcomes. The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, targeting an A1c level <6.0% in the intensive intervention arm, reported an increased risk of CVD death for intensive versus conventional glycemic control, although it remains unclear whether this effect was related to more hypoglycemic episodes, the use of additional hypoglycemic medicines, or to the target glycemic level itself. Likewise, the modest gains in intermediate outcomes in the intensive treatment arms of the Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation (ADVANCE) and the Veterans Affairs Diabetes (VADT) trial were counterbalanced by a twofold to threefold higher risk of severe hypoglycemia. Together, these trials indicate that glycemic control is extremely useful up to a point, but more aggressive glycemic control may be harmful. Similarly, for blood pressure control, 2014–2015 recommendations by the guideline-writing groups endorse less intensive and more individualized blood pressure targets for diabetes and CKD than in the past. Persons with diabetes and CKD require multidisciplinary management involving a combination of treatments and behavioral adjustments to delay progression of CKD and to prevent the associated complications. The Steno-2 study, a landmark prospective, randomized trial in Denmark, demonstrated that compared with conventional treatment, intensive multifactorial intervention led to 46% lower death rate, 56% less severe albuminuria, 43% lower incidence of diabetic retinopathy, and 47% lower incidence of autonomic neuropathy during the 13.3-year study period.