Microalbuminuria: a common, independent cardiovascular risk factor, especially but not exclusively in type 2 diabetes

Microalbuminuria (defined as an albumin-creatinine ratio of 10-25 mg/mmol on the first-morning urine sample, or an albumin excretion rate of 20-200 microg/min on a timed collection) is present in 20-30% of all patients with type 2 diabetes, and is especially common in those with hypertension, endothelial dysfunction and other features of insulin resistance. Although microalbuminuria is predictive of worsening microvascular disease in the kidney (5-10% per year progress to overt diabetic nephropathy), an increased albumin excretion rate (AER) reflects a generalized abnormality of vascular function and is associated with 2-4-fold increases in cardiovascular and all-cause mortality. The extent to which microalbuminuria is a risk factor independent of other variables in type 2 diabetes, e.g. blood pressure and smoking, has been highlighted by recent cohort studies, e.g. the Heart Outcome Prevention Evaluation study and the Wisconsin Epidemiological Study of Diabetic Retinopathy. In the former study, for example, microalbuminuria at baseline increased the adjusted relative risks (RR) of a major cardiovascular event (RR 1.83), all-cause death (RR 2.09) and hospitalization for heart failure (RR 3.23) in both diabetic and non-diabetic subjects. These studies also highlighted that AER is a continuous risk factor, and that levels of AER below the arbitrary threshold for defining microalbuminuria are associated with relatively increased cardiovascular risk. Similarly, microalbuminuria affects 10-15% of middle-aged non-diabetics and is associated with coronary, peripheral and cerebral vascular complications. Detection of microalbuminuria, especially in type 2 diabetes, signifies the need to intensify blood pressure control as part of a multiple risk factor intervention strategy in a high-risk group. As hypertensive patients with type 2 diabetes are frequently treated by more than one antihypertensive agent, ACE inhibitors and low-dose diuretics are preferably recommended in order to provide sufficient blood pressure control and target organ protection.