Microalbuminuria: What Is It? Why Is It Important? What Should Be Done about It?

Microalbuminuria (MA) is defined as persistent elevation of albumin in the urine, of 30–300 mg/day (20–200 μg/min). These values are less than the values detected by routine urine dipstick testing, which does not become positive until protein excretion exceeds 300–500 mg/day. Use of the albumin‐to‐creatinine ratio is recommended as the preferred screening strategy for all diabetic patients. MA is measured in spot morning urine obtained from the patient in the office and sent for measurement of both albumin and creatinine. A value above 0.03 mg/mg suggests that albumin excretion is above 30 mg/day and therefore MA is present. MA should be checked annually in everyone, and every 6 months within the first year of treatment to assess the impact in patients started on antihypertensive therapy. MA is an established risk factor for renal disease progression in type 1 diabetes and its presence is the earliest clinical sign of diabetic nephropathy. In addition, a number of studies suggest that MA is an important risk factor for cardiovascular disease and defines a group at high risk for early cardiovascular mortality in both type 2 diabetes and essential hypertension. MA also signifies abnormal vascular permeability and the presence of atherosclerosis. Among nondiabetic patients with essential hypertension, MA is associated with higher blood pressures, increased serum total cholesterol, and reduced serum high‐density lipoprotein cholesterol. Thus, taken together these data support the concept that the presence of MA is the kidney's notice to the physician/patient that there is a problem with the vasculature. MA can be reduced, and progression to overt proteinuria prevented, by aggressive blood pressure reduction. The National Kidney Foundation recommends that blood pressure levels be maintained at or below 130/80 mm Hg in anyone with diabetes or renal disease. This should be accomplished with antihypertensive agents that prevent the rise in MA and hence prevent development of proteinuria. Such agents are angiotensin‐converting enzyme inhibitors, angiotensin receptor blockers and, to a lesser extent, β blockers, non‐dihydropyridine calcium antagonists, and diuretics. In summary, the presence of MA is a marker of endothelial dysfunction and a harbinger of markedly enhanced cardiovascular risk. All patients with diabetes and/or hypertension should be screened for the presence of microalbuminuria with use of spot morning urine. To maximize prevention of MA development, the following goals should be instituted: 1) blood pressure should be maintained at <130/80 mm Hg and a low‐salt, moderate‐potassium diet instituted; 2) in diabetics, HbA1c should be kept at <7%; 3) in obese patients, a weight loss program should be implemented, with a goal BMI of <30; and 4) the physician and patient, working together, should maintain low‐density lipoprotein cholesterol at <120 mg/dL, and <100 mg/dL if diabetes is present.