Proteinuria (protein in the urine)

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Proteinuria (protein in the urine)

Proteinuria is the presence of protein in the urine. Under physiological conditions, the passage of proteins through the glomerular filter is determined by the pore size of the basement membrane, the molecular weight of the protein (MW), the shape and electric charge of its molecules, and the relationship between the concentration of protein in plasma and filtrate.

However, the presence of protein in the urine does not mean that this protein is of renal origin. Proteinuria is a cardinal symptom of kidney disease, but it can also indicate a pathological condition of the body. The increase in proteinuria depends on:

  • lesions of the basement membrane and podocytes (nephron capsule cells)
  • failure of tubular reabsorption
  • filtration of pathological proteins (paraproteins) with a low molecular weight, which, due to their large amount or due to their qualitative characteristics, are not completely reabsorbed
  • increased secretion of proteins (mucus) by the epithelium of the kidneys, urinary tract, auxiliary glands


Types of proteinuria

There are several types of proteinuria:

  1. Prerenal proteinuria
  2. Renal proteinuria
  3. Postrenal proteinuria


Prerenal proteinuria

Prerenal proteinuria is characterized by the entry into urine through an intact renal filter of abnormal low MW plasma proteins.

Prerenal proteinuria is observed when:

  • monoclonal gammopathies due to increased synthesis of immunoglobulin light chains
  • hemolytic anemias with intravascular hemolysis of erythrocytes
  • for necrotic, traumatic, toxic, and other muscle injuries accompanied by myoglobinemia and myoglobinuria

These conditions only at low concentrations and the very beginning do not cause damage to the renal nephron. High concentrations and/or a long-term pathological process sooner or later leads to an impaired renal filter and the development of acute renal failure.


Renal proteinuria

Renal proteinuria is divided into:

  1. Functional proteniuria:
    • transit
    • working or tension
    • stagnant
    • febrile and toxic
    • orthostatic
    • hyperlordous
  2. Organic proteinuria due to damage to the renal nephron.

Functional proteinuria is observed more often at the age of 20-30 years. The concentration of urine protein in functional proteinuria is usually not massive.

When transient - the release of protein does not exceed 1-2 g / day. Stagnant proteinuria is characterized by a decrease in the amount of urine with a high density in the presence of protein 1-2 g / l, sometimes even higher (up to 10 g / day). Impaired hemodynamics (ischemic proteinuria) develops as a result of a change in the electrical charge of albumin molecules adsorbed on the pores of the membrane and is accompanied by albuminuria.

Ischemic proteinuria can occur with cardiac decompensation, congestion, pregnancy.

Proteinuria of extrarenal origin can appear with myocardial infarction, apoplexy, craniocerebral (TBI) injury, epileptic seizure, colic, fever, in the postoperative period and disappears after the removal of the cause.

Organic proteinuria can be of glomerular and tubular origin.

Glomerular (glomerular) proteinuria develops as a result of damage to the glomerular filter, resulting in impaired filtration and diffusion in the glomeruli.

Glomerular proteinuria is observed in all kidney diseases occurring with glomerular damage:

  • acute and chronic glomerulonephritis
  • diabetes
  • kidney tumor
  • toxicosis of pregnant women
  • nephrosis
  • gout
  • kidney cyst
  • chronic potassium deficiency
  • collagenoses
  • hypertonic disease

Tubular (tubular) proteinuria is caused by inhibition or insufficiency of the enzyme systems of the renal epithelium as a result of toxic effects.

Tubular proteinuria develops with hereditary (congenital) or acquired tubulopathies:

  • acute and chronic renal failure
  • acute and chronic pyelonephritis
  • tubular nephropathies caused by poisoning with heavy metals (mercury, lead), toxic substances, and nephrotoxic drugs

Depending on the integrity of the basement membrane and its ability to pass protein into the urine, there are:

  1. Selective proteinuria
  2. Non-selective proteinuria

Selective proteinuria, in turn, is divided into high-, moderate- and low-selective.

Selective proteinuria is characterized by the selective ability of the basement membrane, in which proteins of low MW (albumin, transferrin) are filtered.

With low-selective proteinuria, not only low-molecular-weight but also high-molecular proteins pass into the urine. Low-selective proteinuria is observed with pronounced lesions of the glomeruli, for example, with chronic nephritis in the acute stage.

The subacute course of the disease is more characterized by moderately selective proteinuria.

Microalbuminuria is the excretion of 30 to 300 mg of protein in the urine per day; it is noted when the filtration of albumin in the glomeruli is impaired and is a criterion for early nephropathy in diabetes.


Postrenal proteinuria

Postrenal proteinuria is possible as a result of the secretion of proteins (mucoids) by the epithelium of the urinary tract. An insignificant protein is made up of dead blood cells, including erythrocytes in the form of microhematuria with urinary stones passing through the urinary tract, epithelial cells of the urinary tract, and neoplasms, mucus.