Microalbuminuria--a biomarker of renal microvascular disease.

Microalbuminuria (amount greater than 30-300 mg/day) reflects an abnormal glomerular capillary permeability to protein. It is usually dependent upon three mechanisms. First, loss of negatively charged surface of the glomerular capillary wall secondary to circulating toxic substances injury-namely, oxidative stress and proinflammatory cytokines-allows the albumin with negatively charged surface to freely escape into the urine. Second, intraglomerular hypertension and hemodynamic maladjustment secondary to glomerular endothelial dysfunction increases filtration pressure and enhances sized selective proteinuria leakage. Third, podocyte injury leads to a vicious cycle of hemodynamic maladjustment and endothelial and podocyte injuries. All three of these mechanisms induce glomerular endothelial injury and microalbuminuria, which reflects renal microvascular disease.