Proteinuria

Under proteinuria is defined as the excessive excretion of proteins ( coll: protein ) in the urine. The limit for a normal (physiological ) protein excretion is set at less than 150 milligrams per day. An increased protein excretion may be a harmless, temporary event and is then referred to as benign reversible proteinuria. However Persistently elevated levels of protein in the urine are not only the consequence of various diseases, but also an important independent cause of the progression of kidney disease.

Basics

An important function of the kidneys is to filter the blood plasma, this occurs in the glomeruli of the renal corpuscles. Proteins from a molecular mass of 80 kilodaltons (kDa ) - for example globulins - are retained by these " filters ". In contrast, substances pass up to a molecular mass of 6-15 kDa that barrier. In addition to this size selectivity there is also a charge selectivity, which retains highly negatively charged proteins.

Albumin with its molecular mass of 66-69 kDa is retained to 99.97. The sieving coefficient for albumin thus is less than 0.001. Base is the strong negative charge of the albumin molecule that prevents an increased filtration. For equal-sized molecules with absent or even positive charge of the glomerular filter is permeable.

The coming into the primary urine proteins are divided into macro-and micro -molecular proteins, although the limit when albumin or its molecular mass is pulled. These proteins are reabsorbed in the proximal tubule to 96 percent. Recording will take place through the mediation of the receptors of the megalin - cubilin complex as a specific ATP-dependent endocytosis. It thus arrive under physiological conditions small amounts of protein in the final urine.

Pathophysiology

The causes of pathological proteinuria are changes that come to fruition in the actual urine formation or have nothing to do with this yourself. The former are, the latter divided as renal glomerular and tubular proteinuria in forms in prerenal (or preglomerular ) and postrenal forms.

The prerenal lying causes lead to an oversupply of proteins and thus to a so-called Überlaufproteinurie. With these pathologically increased concentrations of ( low molecular weight ) proteins in serum occurs consequently to an increased filtration and exceeding the capacity for absorption of these proteins in the proximal tubule of the nephron.

A localized in the glomerular disorder - usually it involves an inflammation ( glomerulonephritis ) - causes a permeable filter so that the absorption capacity in the tubule is also exceeded.

Any failures in Tubuluszellfunktion the reabsorption of proteins is primarily affected. Even normal concentrations of proteins in the primary urine, leading to a significant proteinuria.

In post- renal disorders, the proteins from the urinary tract originate.

At a protein excretion in the urine of more than 3 to 3.5 g per 24 hours in children greater than 1 g per square meter of body surface area and 24 hours, is referred to a so-called large proteinuria. This usually leads to the formation of nephrotic syndrome.

Etiology

The reason for the emergence of a large proteinuria are:

  • Acute and chronic glomerulonephritis
  • Metabolic disease such as diabetes mellitus
  • System diseases such as amyloidosis, systemic lupus erythematosus, inter alia,
  • Cardiac and vascular causes, v. a arterial hypertension
  • Hematologic disorders such as sickle cell anemia
  • Congenital disorders such as congenital nephrotic syndrome or Alport syndrome
  • Complications of pregnancy such as preeclampsia
  • A kidney transplant
  • Chronic graft rejection
  • Drugs
  • Poisons
  • Allergens
  • Microorganisms, viruses

Components

In addition to the amount and the composition of the proteins of importance. So can also be present in minor proteinuria a disease when a pathological distribution pattern is present. This is especially true in systemic diseases such as diabetes mellitus, arterial hypertension, or systemic lupus erythematosus.

From 500 present in the urine of healthy persons proteins, a majority of which is not yet identified, sensitive measuring methods such as radioimmunoassay or nephelometry remedy.

The major urinary proteins are

  • Albumin,
  • Globulin ( alpha-1 and alpha -2 microglobulins, macroglobulins )
  • Uromodulin ( Tamm - Horsfall protein = ), quantitatively the most important physiological protein formed in the kidney,
  • Antibody light chains ( kappa and lambda light chains).

Albumin

Albumin can be excreted increased as a lack of tubular reabsorption as in disorders of glomerular filtration. A clinically isolated albumin excretion is as albuminuria, but the designated common Harnstreifen not ascertainable, at a diabetes clinically significant minor albumin excretion as microalbuminuria.

Medical importance

People in whom an increased excretion of albumin is detected in urine, have an increased risk of suffering later in a progressive loss of renal function to a dialysis-dependent renal failure. For a given renal function increases with increasing proteinuria, the mortality and the risk of suffering a heart attack.

Adenosine triphosphate Chronic kidney disease Digital Object Identifier The Lancet JAMA (journal)
42920
de