I. What is proteinuria?
Normal human urine contains only a small amount of proteinuria, about 20-80mg of urine protein excreted daily, if the urine protein qualitative test is positive or the urine quantitative test exceeds 150mg/24h, it is called proteinuria.
Why does proteinuria occur?
1, damage to the glomerular filtration membrane or increased permeability.
2.Decreased renal tubular reabsorption.
3.Increased protein spillover.
4, increased excretion of renal tubules and urothelial cells.
5. destruction of renal tissue.
6, the effect of body position and exercise.
3. What are the common causes of proteinuria?
1.Transient: seen in exercise, fever or dehydration.
2.Postural proteinuria: classified as transient or persistent.
3, persistent benign proteinuria.
4, primary and secondary glomerulonephritis: such as acute glomerulonephritis, chronic glomerulonephritis, hereditary nephritis, nephrotic syndrome, IgA nephropathy, lupus nephritis, purpura nephritis, etc.
5.Primary tubulointerstitial disease: such as reflux nephropathy, renal dysplasia, acute interstitial nephritis, etc.
Fourth, how to distinguish between true and pseudoproteinuria?
Pseudoproteinuria is commonly found in.
1, mixed with semen or prostate fluid, blood, pus, inflammatory or tumor secretions, as well as menstrual blood, leukorrhea, etc., routine urine protein qualitative examination can show a positive reaction, urine sediment can be seen in a large number of red and white blood cells and flat epithelial cells without tubular type, the urine will be centrifuged and precipitated or filtered, the protein qualitative examination will be significantly reduced or even turned negative.
2, urine for a long time or after cooling, can precipitate salt crystals, so that the urine is white cloudy, easy to be mistaken for protein urine, but heating or adding a little acetic acid can make cloudy urine to clear, to help distinguish.
3.Some drugs such as rifampin and Sandoval can make the urine cloudy and similar to proteinuria when they are excreted from the urine, but the qualitative reaction of proteinuria is negative.
4.Lymphatic urine: when lymphatic urine contains less protein, it is not necessarily chylomicronous.
V. How to determine whether proteinuria is physiological or pathological?
1.Physiological proteinuria
(1) Functional proteinuria
It is usually temporary, and the amount of urine protein is usually less than <1g/24h. Proteinuria is mainly medium-molecule albumin, which occurs after strenuous exercise or during fever, excessive cold, high-temperature work, mental tension and other states of high sympathetic excitement, etc. After the cause is removed, proteinuria can disappear.
(2) Postural proteinuria
Generally less than <1g/24h, we can compare the urine before waking up in the morning after lying in bed at night and the urine after standing for 4-6h for qualitative protein examination, and measure it for 3 consecutive days. It is caused by the left superior mesenteric artery and the angle of the abdominal aorta compressing the left renal vein in the upright position, which increases the pressure of the left renal vein.
(3) Post-exercise proteinuria
Proteinuria occurs after exercise in normal individuals. The intensity of exercise is the main factor in determining proteinuria, and the highest peak of urinary protein amount usually occurs within 0.5h after the cessation of exercise.
2.Pathological proteinuria
It refers to proteinuria caused by various primary or secondary renal diseases and hereditary diseases, characterized by persistent non-resolution of urinary protein, or accompanied by hematuria, swelling, hypertension and other manifestations; it can also present simple proteinuria without any clinical symptoms or signs.
(1) Glomerular proteinuria
It is caused by the increased permeability of the glomerular filtration membrane to plasma protein.
It is the most common type of glomerulonephritis in the clinical setting and can be seen in a variety of primary or secondary glomerulonephritis.
It is caused by ischemia, toxicity, immunopathological damage that disrupts the integrity of the filtration membrane, or by a weakened charge barrier of the filtration membrane.
This type of proteinuria is characterized by a large amount of protein, ranging from 1 to 30 g/d, and by a predominance of albumin, or albumin and proteins of greater molecular weight than albumin.
(2) Renal tubular proteinuria
It is due to impaired reabsorption of filtered protein by the renal tubules.
It is seen in tubulointerstitial lesions, pyelonephritis, congenital tubulopathy, and hypokalemic nephropathy.
This type of proteinuria is characterized by a small amount of total urinary protein, usually <1g/d; and contains only a small amount of albumin, and is dominated by low molecular weight lysozyme, β2-microglobulin, light chain protein, vitamin A binding protein, etc.
(3) Overflow proteinuria
Proteinuria is caused by an abnormal increase of some lower molecular weight (<60-70,000) proteins in the blood circulation, which are filtered out by the glomerulus and exceed the reabsorption capacity of the renal tubules.
This type of proteinuria is seen in patients with multiple myeloma (with native-periodic protein in the urine), myoglobinuria in severe crush injuries, and lysozyme urine in myeloma and monocytic leukemia.
The characteristics of this type of proteinuria.
(i) is the presence of a primary condition causing abnormal plasma proteinemia.
(ii) is the detection of specific proteins by qualitative analysis of urine proteins.
(3) Early glomerular function is normal.
(4) Secretory proteinuria
It refers to proteinuria caused by protein or other proteins secreted by the renal tubules and lower urinary tract.
For example, the renal tubules secrete IgA or large-molecule Tamn-Horsfall protein after inflammation or drug stimulation, which is the substrate for the formation of tubular urine and may also be related to the immune response, but the amount is not large.
Mucin is due to pus, blood and secretions produced by urinary tract infection and prostatic fluid, semen or mixed with vaginal secretions, and the amount is usually small.
(5) Tissue proteinuria
There are some soluble metabolites of tissue decomposition in normal urine, the content is small, but when poisoning, ischemia, inflammation or tumor leads to its tissue necrosis, the content can increase.
For example, glomerular basement membrane antigen is excluded from the urine in glomerulonephritis, and specific antigenic substances related to mid-stream can be detected in the urine in tumor.
VI. How to determine the degree of proteinuria?
Mild proteinuria: 24h urine protein quantification less than 1g.
Moderate proteinuria: 24h urine protein quantification in the range of 1.0-3.5g.
Severe proteinuria: 24h urine protein quantification is more than 3.5g.
VII. Quantification of proteinuria and inference of etiology?
1.The quantification of renal tubular urine protein is usually less than 2.0g/d. When the quantification of urine protein is higher than 2.0g/d, there is usually proteinuria caused by glomerular lesions.
2, when the quantitative urine protein is greater than 3.5g/d and accompanied by hypoproteinemia, it is called “nephrotic syndrome”, and the cause of this condition is also mostly glomerulopathy.
3. if there is significant edema, low plasma albumin, decreased a1 and r globulins, increased a2 globulins, increased B globulins and fibrin, increased serum cholesterol, phospholipids and lipoproteins – in nephrotic syndrome.
4. if accompanied by edema, hematuria, hypertension, tubuluria, etc.-mostly acute and chronic glomerulonephritis, secondary glomerular disease, renal arteriosclerosis, etc.
5. if accompanied by symptoms of urinary tract irritation, increased leukocytes in the urine sediment, the presence of pus urine, leukocyte tubuluria, urine culture with pathogenic bacteria – seen in pyelonephritis.
6. hyperuricemia – seen in gouty nephropathy or leukemia invading the kidneys.
7. proteinuria after the application of antibacterial drugs, analgesics or other chemicals – considered to be drug-related kidney damage.
8. If a young patient with nephritis has deafness, eye abnormalities and a family history of the disease – consider hereditary nephritis.