Background: The transition of albumin from the vascular lumen into the surrounding tissue always indicates a serious disturbance of the vascular wall. Clinically, this process can be recognized as "cotton-wool" spots of the retina or by testing the urine for the presence of albumin. The appearance of albumin in the urine is pathologic and should be evaluated within the context of the accompanying cardiovascular risk.
Pathophysiology and definitions: Albumin transition is indicative of a disturbance of the barrier function of endothelial cells. In the kidney, damage to podocytes, mesangial and endothelial cells, a loss of charge selectivity, and an altered expression of matrix proteins can be observed. However, vascular alterations are not confined to the kidney but can also be observed in the myocardium. Even though thresholds for microalbuminuria (> 30 mg/24 h) and proteinuria (> 300 mg/24 h) have been arbitrarily defined, an increase in risk starts at much lower levels of albumin excretion.
Prevalence and prognostic importance: The prevalence of microalbuminuria in the general population is about 8%. However, prevalence rates of > 50% have been observed in high-risk groups, which are accompanied by an increased risk for cardiovascular morbidity and mortality.
Therapeutic options: A number of therapeutic options (tight blood sugar control, blood pressure reduction, lipid lowering) lead to a reduction of albuminuria and an improvement in cardiovascular prognosis. This has particularly been described for renin-angiotensin-aldosterone system-(RAAS-)blocking agents. Their use is not only associated with a reduced risk of end-organ damage (heart failure, diabetic nephropathy, cerebrovascular events) but has been described to decrease mortality as well.
Recommendation: A timely diagnosis, a consecutive cardiovascular diagnostic work-up and the subsequent use of RAAS-blocking agents is indicated in patients in whom albuminuria has been diagnosed.