Microalbuminuria

Microalbuminuria refers to the secretion of low levels of albumin ( 20 to 200 mg / l or 30 to 300 mg per day) in the urine. People with diabetes or hypertension microalbuminuria is found in about 10 to 40% of those affected. In the general population the incidence of microalbuminuria is about 5 to 7%. The level of albuminuria is an independent risk factor for the later occurrence of kidney disease, from cardiovascular diseases such as heart attack, stroke or circulatory disorders and increased mortality. Therapies that reduce albumin excretion, reduce the risk of cardiovascular disease. Individual differences in the levels of albumin excretion are detectable shortly after birth and probably reflect individual differences in the function of endothelial cells, the innermost cell layer of blood vessels, resist.

Definition

Normally, the kidneys excrete 20 mg albumin per day in the urine ( Normalbuminurie ). Excretion of 30 to 300 mg of albumin in 24 hours is referred to as microalbuminuria, the excretion of more than 300 mg of albumin in 24 hours as macroalbuminuria or proteinuria.

Proof

Microalbuminuria is not detectable using conventional urine test strips. Conventional Rapid tests detect only urine excretion of more than 300 to 500 mg of albumin per day. For the detection of microalbuminuria are various antibody - based detection methods: radioimmunoassay, nephelometry, turbidimetry and ELISA immune. HPLC can also be detected albumin which does not react with antibodies. Goldstandard_ ( method ) is the determination of albumin in the urine was collected over 24 hours. Simultaneous determination of albumin and creatinine and calculation of the albumin - creatinine ratio may be waived collecting the urine: Microalbuminuria is defined by an albumin / creatinine ratio of 30 to 300 mg / g, macroalbuminuria by an albumin / creatinine ratio > 300 mg / g For early detection test strips are used for antibody-based semi-quantitative detection of low concentrations of albumin in the urine.

Pathophysiology

Albumin is a relatively large, negatively charged protein ( molecular mass 69 kDa, size 36 Å). Before albumin passes into the urine, it must pass through the capillary wall in the glomeruli ( glomerulus ). The endothelial cells of the renal corpuscle have on the cell membrane, a highly negatively charged glycocalyx. The pores of the glomeruli form a size-and charge- specific filtration barrier and prevent the negatively charged albumin in the passage. 99% of albumin, which still crosses the blood - urine barrier is determined by the cells in the anterior part of the renal tubule, the proximal tubule cells recovered ( reabsorbed ) and degraded. High blood pressure and diabetes increase the pressure in the glomerulus, thus increasing the amount of filtered albumin. In addition, a high blood sugar (hyperglycemia ) decrease the negative charge of the glomerular capillary endothelial cells, thus increasing the permeability of the blood - urine barrier for albumin. Exceeds the amount filtered albumin to the capacity of the cells of the proximal tubule to the reabsorption, or if it is reduced due to damage to the proximal tubular cells, albumin excretion increases in the urine, it comes first for microalbuminuria and with further increasing degradation to macroalbuminuria or proteinuria.

Epidemiology

At 20 to 40% of diabetics in which no renal disease is known, it can be shown microalbuminuria ( prevalence). Per year occurs in 2 to 2.5 % of diabetic patients with normal albumin excretion for the first time on microalbuminuria (incidence). Type 1 diabetics are particularly at risk if they have an increased waist circumference.

In patients with hypertension, microalbuminuria is detectable at about 8 to 23 % of those affected. In the general population there is a microalbuminuria in 5-7 % of the examined persons.

Microalbuminuria as a risk factor

In patients with diabetes, the occurrence of microalbuminuria marks the transition from the early stage of renal involvement with increased glomerular filtration rate ( stage of hyperfiltration ) in the stage of increasing renal function loss. In people who do not have diabetes, microalbuminuria has a indicate an increased risk of developing in the next few years of overt renal disease.

Diabetic patients with microalbuminuria have an approximately 2.4 -fold increased risk of dying from cardiovascular complications compared to diabetic patients with normal albumin excretion. Even in people with high blood pressure ( hypertension ) and in the general population is at detection of microalbuminuria is a risk within the next five years of suffering from cardiovascular disease ( morbidity) or increases of dying (mortality). In addition, microalbuminuria increases the risk of developing dementia or venous thromboembolism.

Even if the albumin excretion within the normal range (albumin / creatinine ratio <25 mg / g ) is still higher values ​​are associated with an increased risk of developing hypertension in later life.

Screening

Testing for microalbuminuria is used in diabetic patients for early detection of renal involvement. In patients with hypertension the detection of microalbuminuria to identify the individuals serving with an increased cardiovascular risk who benefit from a more intensive treatment of hypertension.

Therapy

ACE inhibitors and AT1 antagonists can prevent the re- occurrence of microalbuminuria and improve microalbuminuria in patients with diabetes and hypertension in diabetic patients. A decrease in albumin excretion leads to a reduction in the risk of developing cardiovascular diseases.

Guidelines

The guidelines of the National Kidney Foundation of the USA recommends to examine patients with diabetes annually for the presence of diabetic nephropathy, immediately after diagnosis of type 2 diabetes and from the 5th year after diagnosis of type 1 diabetes. If a micro-or macroalbuminuria found in 2 of 3 urine samples, there is a chronic renal injury. Diabetic nephropathy is almost certainly caused in macroalbuminuria, microalbuminuria after at least 10 years duration of type 1 diabetes or microalbuminuria and coexisting diabetic retinal damage (diabetic retinopathy). In diabetic nephropathy should be treated with an ACE inhibitor or an AT1 antagonist. Blood pressure should be set to values ​​below 130/ 80 mmHg.

The guidelines for the diagnosis and treatment of arterial hypertension of the German Hypertension League recommend the determination of microalbuminuria in all diabetics and, where possible, also in non-diabetic patients with hypertension. For detection of microalbuminuria an aggressive lowering of blood pressure and a drug blockade of the renin -angiotensin system are recommended.