What is meant by microalbuminuria? Microalbuminuria (MAU) is defined as albumin in the urine that is outside the reference range for healthy individuals. It is defined as 30-300mg of albumin excreted in the urine in 24 hours, or 20-200ug/min. A urinary albumin/creatinine ratio (ACR) of 10-25mg/mmol or 30-300mg/g is also used. If the urinary albumin is >300mg/24h it is said to be massive albuminuria. Sun Jiefeng, Department of Nephrology, Tangdu Hospital, Fourth Military Medical University Why is MAU an early warning radar? MAU is a sensitive indicator reflecting that the kidney is affected by hemodynamics and many metabolic factors, such as disorders of glucose metabolism, dyslipidemia, hypertension, etc. It is also called early renal function because it appears well before the irreversible damage of renal parenchyma and abnormal renal function (serum creatinine). It is now believed that MAU not only represents impaired glomerular endothelial cell function but also is an important marker of systemic vascular endothelial cell damage. Therefore, MAU is often combined with multiple cardiovascular risk factors or cardiovascular diseases, as well as abnormal glucose tolerance, hyperinsulinemia and hypertension, and is strongly associated with an increased risk of total death, cardiovascular death and premature death, and is now more commonly considered to be an independent risk factor for cardiovascular disease. Therefore, it is called an early warning radar for human health, especially for heart, brain and kidney diseases! In this article, we will briefly review the relationship between the development of MAU and kidney disease, especially chronic kidney disease and high risk factors for chronic kidney disease: diabetes and hypertension. Mechanism of MAU formation and incidence 1, normal glomerular basement membrane has 3-4nm micropores with a layer of negative charge, i.e. with aperture screen and charge barrier, so that negatively charged medium and large molecules of proteins in plasma are not easy to pass. 2, Albumin (Albumin) molecular weight of 69kD, is a large molecule protein with negative charge, is the highest content of plasma protein, average 44g / L, radius of about 3.6nm, under normal circumstances only a small amount of albumin filtration, and 95% of albumin and in the proximal tubule is reabsorbed. Clinically, once there is an increase in human capillary bulb pressure, an increase in glomerular filtration membrane filtration pore size, a decrease in charge barrier, a decrease in tubular reabsorption capacity and an increase in plasma small and medium molecular weight proteins, the amount of albumin excreted in the urine will increase and micro or clinical proteinuria will occur. 3. The mechanism of the increased excretion of microalbuminuria may be related to the abnormal synthesis of heparan sulfate on the basement membrane. Heparan sulfate molecules with many anionic side chains play an important role in maintaining the basement membrane charge and pore size. 4, Alterations in renal hemodynamics are also important in inducing microalbuminuria. Diabetic patients are often accompanied by glomerular vascular regulation dysfunction and changes in renin-angiotensin (RAS), which cause altered glomerular permeability. Diabetes mellitus with hypertension is more likely to lead to glomerular vascular damage, resulting in microalbuminuria. 5, In addition, the analysis of microalbuminuria in normal population shows that there is a tendency to increase microalbuminuria discharge with age, but this change is still within the range of healthy people. 6.According to a Dutch-Australian study, 16.6% of the overall population had normal high values (10-20 mg/L) of albuminuria and 6-7.2% had MAU (20-200 mg/L). 7, The prevalence of MAU in the overall population, hypertension, diabetes, metabolic syndrome and obesity was 7.33%, 14.71%, 17.86%, 12.79% and 7.99%, respectively. 8, In a study of relatives of MAU patients, the incidence of MAU was also found to be higher than that of non-relative controls. 9, As the mechanisms of MAU continue to be explored, studies now suggest that genetic and ethnic factors that regulate the RAS system, low birth weight associated with inadequate renal unit development, and environmental factors associated with susceptibility to chronic kidney disease may also be important factors in the development of MAU. Please pay attention to MAU as an early change of the disease, which has important value and clinical significance for early diagnosis and early treatment of the disease!