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Back to Nephrology Articles

Article author: Dr. Riham Z Fardoun, Pharm.D. Pharmacy Doctor; Research and Teaching Assistant at the University of Houston, College of Pharmacy, Heart and Kidney Institute; Texas, United States.

Wednesday 15th March, 2006

   
 
Dr. Riham explains how annual screening for microalbuminuria in diabetics will allow the early identification of nephropathy.
 

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Diabetes has become the most common single cause of end-stage renal disease (ESRD) in the United States and worldwide. This is due to the fact that diabetes, in particular type 2 diabetes, is increasing in prevalence and patients with diabetes are living longer.

It has been estimated that approximately 45 % of new patients receiving dialysis in the United States are diabetics. Early diagnosis of diabetes and early intervention are critical in preventing the progression towards renal failure seen in many type 1 and a significant percentage of type 2 diabetics.

The earliest clinical evidence of diabetic nephropathy is the presence of microalbumiuria, defined as the appearance of low but abnormal levels (greater than 300 mg in a 24-hour collection) of albumin in the urine. Clinically, diabetic nephropathy is characterized by a progressive increase in proteinuria and decline in GFR, hypertension, and a high risk of cardiovascular morbidity and mortality. Thus, the finding of microalbuminuria should trigger screening for possible vascular diseases and aggressive intervention to reduce all cardiovascular risk factors in patients with diabetes type 1 and 2.

The natural history of diabetic nephropathy is a process that progresses gradually over years. Microalbuminuria typically occurs after 5 years in type 1 diabetes, and ESRD develops in 50% of type 1 diabetics. On the other hand, type 2 diabetes has a more variable course. Patients often present at diagnosis with microalbuminuria because of delays in diagnosis and other factors affecting protein excretion. Fewer patients with microalbuminuria progress to advanced renal disease. Without intervention, approximately 20% develop ESRD. However, because of the high prevalence of type 2 compared to type 1 diabetes, the majority of diabetics on dialysis are type 2 diabetics.

Many factors account for the pathophysiology in diabetic nephropathy. First, structural and anatomical changes in the kidney lead to increased glomerular capillary pressure in diabetes, and this increase is associated with hyperfiltration at the glomerulus. Second, glucose can induce the formation of advanced glycosylation end products (AGEs) by binding irreversibly to proteins in kidney and circulation. Over years these formed AGEs can stimulate growth and fibrotic factors, which contribute to the overall renal damage. Third, angiotensin 2, itself contributes to the progression of diabetic nephropathy by constricting the efferent arteriole in the glomerulus, and consequently leading to higher glomerular capillary pressures.

In screening for diabetic nephropathy, early testing for glucose intolerance and diabetes to identify patients who are at risk for developing microalbuminuria is recommended, particularly if they have other risks for type 2 diabetes such as hypertension, lipid abnormalities, or central obesity. Therefore, the presence of microalbuminuria should be performed at diagnoses in patients with type 2 diabetes. On the other hand, since microalbuminuria rarely occurs with short duration of type 1 diabetes, screening in individuals with type 1 diabetes should begin after 5 years? disease duration. Some evidence suggests that the prepupertal duration of diabetes maybe important in the development of microvascular complications. Therefore, clinical judgment should be exercised when individualizing these recommendations.

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The goal of therapy in diabetic nephropathy involves multi-clinical approaches. One keystone in the prevention and management of diabetic nephropathy is tight glycemic control. The Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) have proved that intensive diabetes therapy can significantly reduce the risk of the development of microalbuminuria and nephropathy in diabetic patients. The American diabetic association recommends an average hemoglobin A1c (HbA1c) value of 7 %.

In addition to glycemic control, blood pressure control is the other keystone in prevention and treatment. The importance of blood pressure control, no matter what agent is used, cannot be emphasized enough in diabetes, both for slowing progression of nephropathy and for preventing cardiovascular morbidity and mortality. Currently, the most recent Joint National Committee guidelines recommends that blood pressure in diabetics be reduced to less than 130/80 mm Hg. It is important for clinicians and patients to be aware early on that three or more agents may be required to achieve the blood pressure goal, and these agents will likely be needed long term. Angiotensin-converting enzyme (ACE) inhibitors or Angiotensin Receptor Blockers (ARBs) are considered first line agents in patients with concomitant hypertension and diabetes. In many cases, diuretics might be added as second-line agents after angiotensin blockade in diabetics. Dihydropyridines , a class of Calcium Channel Blockers (CCB) may best be reserved as third- or fourth-line agents in patients with diabetes, only after angiotensin blockade and diuretics have already been instituted.

Other non-pharmacological approaches involve dietary restriction of protein intake. Dietary restriction of 0.8 g/kg/day in patients with overt nephropathy, or even 0.6 g/kg/day in the face of a falling GFR is recommended. In addition, it is important to maintain a low-sodium diet in diabetic nephropathy. Because many diabetics with renal disease are salt sensitive, minimizing salt intake can help in reaching blood pressure goals, with secondary benefits of decreased stroke risk, regression of left ventricular hypertrophy, and reduction in proteinuria. An advocated low-sodium diet of equal or less than 2.3 grams (5.8 grams of NaCl) or 100 mEq daily in patients with diabetes and either hypertension or any degree of proteinuria is recommended. Furthermore, avoidance of nephrotoxic agents, like Nonsteroidal antiinflammatory drugs (NSAIDs) and Radiocontrast media is advised. Lastly, Referral to a nephrologist should be considered if the GFR is steadily declining or is already below 60-70 ml/min.

In conclusion, annual screening for microalbuminuria in diabetic patients will allow the identification of nephropathy at an early stage. Improving glycemic control and aggressive antihypertensive treatment will slow the rate of progression of diabetic nephropathy. In addition, protein and salt restriction and the avoidance of nepthrotoxic drugs may have benefits in selected patients.

References

American diabetic association.

Remuzzi, G., and Weening, J. 2005. Albuminuria as early test for vascular disease. Lancet. 365:556-557

Xue, J.L., Ma, J.Z., Louis, T.A., and Collins, A.J. 2001. Forecast of the number of patients with end-stage renal disease in the United States to the year 2010. J. Am. Soc. Nephrol. 12:2753-2758.

Lysaght, M.J. 2002. Maintenance dialysis population dynamics: current trends and long-term implications. J. Am. Soc. Nephrol. 13(Suppl. 1):S37-S40.

National Kidney Foundation. K/DOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am. J. Kidney Dis. 39:S1-S266.

Levey, A.S. et al. 1998. Controlling the epidemic of cardiovascular disease in chronic renal disease: what do we know? What do we need to learn? Where do we go from here? National Kidney Foundation Task Force on Cardiovascular Disease. Am. J. Kidney Dis. 32:853-906

Nelson, R.G. et al. 1991. Assessment of risk of overt nephropathy in diabetic patients from albumin excretion in untimed urine specimens. Arch. Intern. Med. 151:1761-1765.

Adler, A.I. et al. 2003. Development and progression of nephropathy in type 2 diabetes: the United Kingdom Prospective Diabetes Study (UKPDS 64). Kidney Int. 63:225-232.

Ruggenenti, P. et al. 2004. Preventing microalbuminuria in type 2 diabetes. N. Engl. J. Med. 351:1941-1951

Peterson, J.C. et al. 1995. Blood pressure control, proteinuria, and the progression of renal disease. The Modification of Diet in Renal Disease Study. Ann. Intern. Med. 123:754-762

de Zeeuw, D. et al. 2004. Proteinuria, a target for renoprotection in patients with type 2 diabetic nephropathy: lessons from RENAAL. Kidney Int. 65:2309-2320.

Tarver-Carr, M., Brancati, F., Eberhardt, M., and Powe, N. 2000. Proteinuria and the risk of chronic kidney disease (CKD) in the United States. J. Am. Soc. Nephrol. 11:168A.

Barnett, A.H. et al. 2004. Angiotensin-receptor blockade versus converting-enzyme inhibition in type 2 diabetes and nephropathy. N. Engl. J. Med. 351:1952-1961.

Mogensen, C.E. 1976. Progression of nephropathy in long-term diabetics with proteinuria and effect of initial anti-hypertensive treatment. Scand. J. Clin. Lab. Invest. 36:383-388.

Tanaka, R., Kon, V., Yoshioka, T., Ichikawa, I., and Fogo, A. 1994. Angiotensin converting enzyme inhibitor modulates glomerular function and structure by distinct mechanisms. Kidney Int. 45:537-543.

 

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