Types and Causes of Proteinuria

Proteinuria means the excretion of protein in the urine. A healthy person does not excrete proteins in the urine or the excretion of proteins is less than 150 mg per day. The proteins most commonly found in the urine are those derived from the plasma of blood and consist of a mixture of albumin and globulin. Predominantly albuminuria (excretion of albumin in urine) is detectable on routine urine analysis during a medical examination. Albuminuria could be organic (due to involvement of kidneys or other organs) or functional (due to physiological or biological stress on kidneys). The functional albuminuria is usually intermittent and not accompanied by any symptoms or evidence of kidney disease. Renal function tests and urinary deposits are found to be normal during the functional albuminuria. It may be connected with posture; being absent when the person is lying down and present when standing. The functional albuminuria usually clears up in early adult life and seems to be associated with the growth and development of kidneys. Any severe stress may also lead to transient albuminuria. Exposure to severe cold and excessive exercise or physical activity may cause functional or transient proteinuria. However, there is nothing to worry about as the functional albuminuria is self limiting with respect to the cause. Mild to moderate functional albuminuria may also be detected during last two months of pregnancy due to pressure on kidneys.

Organic albuminuria is of three types: 1) Renal Albuminuria - When the cause is the kidney disease. 2) Pre-renal Albuminuria - When the kidneys are affected secondarily to some other disease. Post-renal Albuminuria - When the protein is added to the urine after it has left the renal tubules.

1. Renal Albuminuria: It is found in all forms of kidney disease. The cause of renal disorder or kidney disease may be inflammatory (infectious), degenerative (immunological) or destructive (toxic or malignant). The plasma globulin and red blood cells (RBCs) may also be excreted along with albumin during some renal disorders. The urine would be smoky in color if macroscopic hematuria (blood in urine) is also associated with proteinuria. The cases of acute glomerulonephritis may excrete 0.5 to 2.0 percent (0.5 g to 2.0 g/dl) protein in the urine, whereas the cases affected by chronic glomerulonephritis generally excrete less than 0.5 percent (0.5 g/dl) protein in the urine. The amount of protein excreted daily would vary depending on the volume of urine voided daily. The ratio of albumin to globulin excreted in the urine may vary from 10:1 to 5:1. A routine and quantitative urine analysis is required to evaluate the extent of excretion of proteins in the urine.

2. Pre-renal Albuminuria: It is found in a variety of conditions exerting stress on the kidneys. The pre-renal albuminuria usually disappears when the primary disease is cured. Impairment of renal circulation due to dehydration, diarrhea or vomiting, blood loss due to accidental injuries or anemia are the most common conditions, which could lead to pre-renal albuminuria.

3. Post-renal Albuminuria: The proteinuria or albuminuria is termed as post-renal albuminuria if protein is possibly added to the urine as it passes along the urinary tract after leaving the urinary tubules of the kidneys. The major causes of the post-renal albuminuria are the lesions of the renal pelvis or urinary bladder. Lesions of the prostate (in male patients) and urethra also lead to post-renal albuminuria. Admixture of discharges from the vagina (in female patients) and semen (in male patients) may also give positive tests for protein.