Protein in the urine

Protein in urine or proteinuria is a pathological condition when urine contains protein molecules that are normally absent in urine or are found in extremely small quantities. Proteins are the building material for the entire human body, including muscle and bone tissue, all internal organs, hair and nails. Protein also takes part in a very large number of processes occurring in the human body at the cellular and molecular levels. The main function of protein is to maintain oncotic pressure, thus ensuring homeostasis in the body.

The main protein that is most often found in urine is albumin. In case of damage to the kidney glomeruli, the protein begins to pass through the glomerular filter. Albuminuria is the presence of albumin in the urine. The main function of albumin in the blood is to maintain oncotic pressure by retaining water in tissues and intercellular water.

In healthy people, the daily amount of urine contains 50-100 mg of protein.

Proteinuria - the excretion of protein in the urine exceeding 300 mg/day - is one of the most reliable signs of kidney damage.

The causes of protein in urine may be physiological and pathological. Glomerular proteinuria, which occurs due to impaired glomerular membrane permeability, is observed most often; it is one of the most reliable signs of renal parenchyma damage. The severity of proteinuria is used to assess the degree of renal damage activity.

Microalbuminuria - excretion of albumin in urine from 30 to 300 mg/day - is the most sensitive marker of the development of kidney damage in essential arterial hypertension and diabetes mellitus, when its presence reliably indicates the development of diabetic nephropathy.

Clinical evaluation of microalbuminuria in patients with diabetes mellitus

Survey plan

Necessary measures

Regular screening Exclusion of causes of transient microalbuminuria Confirmation of the permanent nature of microalbuminuria

In patients with type 1 diabetes mellitus lasting more than 5 years, the study is carried out every year In patients with type 2 diabetes, the study is carried out when the diagnosis is established, and then every year Abdominal obesity (at least once a year) Exclusion of hyperglycemia, urinary tract infections, physical activity, essential arterial hypertension, chronic heart failure III-IV FC (NYHA)* If microalbuminuria is detected, repeat the test within 3-6 months to confirm its permanent nature.

* NYHA (New York Heart Association) functional classes - functional classes according to the classification of the New York Heart Association.

Microalbuminuria is considered as one of the reliable signs of generalized endothelial dysfunction, which determines an unfavorable prognosis in patients with cardiovascular diseases. In this regard, it is advisable to perform a study on microalbuminuria in risk groups, including the following conditions:

• essential arterial hypertension;
• diabetes mellitus type 1 and 2;
• obesity;
• metabolic syndrome;
• chronic heart failure;
• acute coronary syndrome/acute myocardial infarction.

Beta ₂ -microglobulinuria (normally up to 0.4 μg/l) is observed in tubulointerstitial nephritis, pyelonephritis and congenital tubulopathies.

Myoglobinuria indicates increased catabolism of tissue components, including muscle tissue. It is observed in crush syndrome (Cray syndrome), severe dermatomyositis-poliomyositis. Hemoglobinuria (in particular, when drinking acetic acid instead of alcoholic beverages) and myoglobinuria (in traumatic and non-traumatic forms of rhabdomyolysis) are also observed in individuals who abuse alcohol. Myoglobinuria and hemoglobinuria are precursors to acute hemoglobinuric and myoglobinuric nephrosis; as a result of tubular obstruction by these proteins, acute renal failure develops, which is usually difficult to eliminate.

Increased excretion of immunoglobulin light chains, usually pathologically altered (paraproteins), is a reliable sign of plasma cell dyscrasias (multiple myeloma, Waldenstrom's macroglobulinemia, light chain disease). In multiple myeloma, Bence Jones protein is detected, which is thermolabile: when heated to 56 °C, this substance precipitates, and dissolves again at 100 °C. When cooled to room temperature, Bence Jones protein precipitates again. In plasma cell dyscrasias, overflow proteinuria often acts as the first symptom of the disease, before the detection of characteristic bone changes and the development of a corresponding picture of the peripheral blood smear. In some cases, proteinuria in this group of hemoblastoses precedes changes in cytological preparations of the sternal puncture and iliac crest.

Orthostatic proteinuria is observed at the age of 13-20 years, more often in young men, while other signs of kidney damage are absent.

Proteinuria of tension in healthy individuals, including athletes, occurs after significant (especially dynamic) physical exertion. Protein in urine is detected only in the first portion of urine collected.

Febrile proteinuria develops with fevers with a body temperature of 39-41 °C, mainly in children and the elderly. The diagnosis of febrile proteinuria involves dynamic monitoring of the patient's kidneys.

High levels of urinary protein excretion, especially those resistant to treatment, generally have an unfavorable prognostic value (“Proteinuria and nephrotic syndrome”).

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