I. Classification according to the mechanism of proteinuria
1.Glomerular proteinuria
Increased permeability of the glomerular filtration membrane or changes in glomerular hemodynamics, such as increased pressure in the glomerular capillaries or slowed plasma flow, can cause a large amount of protein to be filtered into the glomerular filtrate, far exceeding the reabsorption capacity of the renal tubules, resulting in proteinuria.
2. Renal tubular proteinuria
Proteinuria caused by the dysfunction of renal tubular reabsorption, which affects the reabsorption of protein in the glomerular filtrate, is commonly caused by various causes of interstitial renal tubular disease.
3.Overflow proteinuria
The glomerular filtration membrane is not damaged, and proteinuria is caused by the increase of abnormal proteins in plasma such as monoclonal immunoglobulin light chain, hemoglobin or myoglobin components, which are easy to overflow from the glomerulus due to their small molecular weight and cannot be completely reabsorbed by the renal tubules.
4.Tissue proteinuria
Normal kidney and urinary tract can secrete some proteins, such as Tamm-Horsfall protein, secretory IgA, fibronectin, enzyme protein, complement, secretion from prostate and seminal vesicles, etc., among which Tamm-Horsfall is more significant in clinical practice.
5.Mixed proteinuria
Proteinuria that appears in both glomerular and tubular lesions is called mixed proteinuria, such as systemic lupus erythematosus that invades both glomeruli and tubules.
II. Classification by protein content
Clinically, it can be divided into nephrotic syndrome type proteinuria and fractional nephrotic syndrome type proteinuria, with the former having a urine protein content greater than 3.5g per day and the latter having less than 3.5g.
Third, according to the molecular weight of urine protein classification
Protein molecules in urine can be divided into small, medium and large molecule proteins. According to the different protein composition of the molecular weight of urine protein, it can be divided into selective and non-selective proteinuria.
Fourth, physiological proteinuria and pathological proteinuria
1, physiological proteinuria is divided into functional and non-functional proteinuria (or upright proteinuria) two categories.
Functional proteinuria causes are
(1) febrile proteinuria
The mechanism may be due to increased renal blood flow and increased glomerular filtration membrane permeability during the febrile period.
(2) Cold and high temperature proteinuria
(3) Exercise proteinuria
(4) bruised proteinuria
It can occur when there is right heart insufficiency, pericardial effusion, or impaired inferior vena cava reflux, and is caused by transient renal venous stasis; upright proteinuria is proteinuria that occurs in the upright position or anterior convexity of the spine, characterized by negative urine protein test before rising in the morning, gradually appearing after getting up and moving around, and then turning negative after lying down at rest, this kind of postural proteinuria is mostly seen in lean and long young people, and the urine protein content is usually The urine protein content is usually less than 1g per day, without hypoproteinemia.
2.Pathological proteinuria
Proteinuria caused by various primary or secondary renal diseases is collectively called pathological proteinuria. It is characterized by persistent proteinuria, and the amount can be more or less.
V. Diagnostic steps
1.Determine whether it is true proteinuria
2.Decide whether the proteinuria is functional or pathological
3.Determine the disease that produces proteinuria.