Excess protein in the urine. Some protein is normal in the urine. Too much means protein is leaking through the kidney, most often through the glomeruli. The main protein in human blood and the key to the regulation of the osmotic pressure of blood is albumin. Proteinuria is synonymous with albuminuria.
People with proteinuria have urine containing an abnormal amount of protein. The condition is often a sign of kidney disease.
Healthy kidneys do not allow a significant amount of protein to pass through their filters. But filters damaged by kidney disease may let proteins such as albumin leak from the blood into the urine.
Proteinuria can also be a result of overproduction of proteins by the body.
Kidney disease often has no early symptoms. One of its first signs may be proteinuria that’s discovered by a urine test done during a routine physical exam.
The glomerulus provides a charge- and size-selective barrier to albumin. The small amount of albumin and non-albumin protein that is filtered is very well reabsorbed in the proximal convoluted tubule (PCT). Damage to this intricate selectivity to albumin has detrimental effects and contributes to sclerosis.
Podocytes are the terminally differentiated epithelial cells of the glomerulus. Crosstalk among podocytes, mesangium, and endothelium maintains the normal filtration barrier. As all three are interlinked, damage to any one of them affects the functioning of the others.
Endothelium activation and loss of selectivity leads to prolonged exposure of podocytes to proteins. This result in the activation of renin-angiotensin in podocyte and alteration of size selectivity. Damage to podocytes in turns leads to decrease in vascular endothelial growth factor (VEGF) required for endothelial fenestrae formation.
The filtration of proteins across the abnormal glomerular capillary wall (GCW) exposes mesangial and tubular cells to these proteins. Mesangial cells lie close to capillary lumen and play an important role in glomerular hemodynamics and immune complex clearance. However, cytokine generation with podocyte damage can lead to mesangial cell activation and proliferation.
The protein-mediated cytotoxicity causes endothelial damage, with podocyte loss leading to the production of chemokines and cytokines that initiate an inflammatory response. The end point is sclerosis and fibrosis of the glomerulus.
You are not able to see protein in your urine. The only way to know if you have proteinuria is to have your urine tested. Most people do not notice any symptoms. If you do have symptoms, they might include foamy urine or swelling in your hands, feet or face.
Proteinuria is a common finding in adults in primary care practice. An algorithmic approach can be used to differentiate benign causes of proteinuria from rarer, more serious disorders. Benign causes include fever, intense activity or exercise, dehydration, emotional stress and acute illness. More serious causes include glomerulonephritis and multiple myeloma. Alkaline, dilute or concentrated urine; gross hematuria; and the presence of mucus, semen or white blood cells can cause a dipstick urinalysis to be falsely positive for protein. Of the three pathophysiologic mechanisms (glomerular, tubular and overflow) that produce proteinuria, glomerular malfunction is the most common and usually corresponds to a urinary protein excretion of more than 2 g per 24 hours. When a quantitative measurement of urinary protein is needed, most physicians prefer a 24-hour urine specimen. However, the urine protein-to-creatinine ratio performed on a random specimen has many advantages over the 24-hour collection, primarily convenience and possibly accuracy. Most patients evaluated for proteinuria have a benign cause. Patients with proteinuria greater than 2 g per day or in whom the underlying etiology remains unclear after a thorough medical evaluation should be referred to a nephrologist.
If your tests show that you have proteinuria, work with your doctor to treat it. Remember, if the cause of your proteinuria is not treated, your kidneys may be damaged further. Treating proteinuria is one way to keep your kidneys as healthy as possible.
Ask your doctor if you should:
- Have other tests to check your kidneys
o The eGFR (estimated glomerular filtration rate) test or a 24-hour urine test can tell your doctor more about how your kidneys are working.
- Take medicines to help protect your kidneys
o Some blood pressure medicines, like ACE inhibitors and ARBs, may help protect your kidneys. Your doctor may prescribe one of these medicines even if you don’t have high blood pressure.
- Take steps to control high blood pressure and diabetes if you have them
o Limiting salt and fat in your diet and getting exercise most days of the week can help.
- See a nephrologist (kidney specialist)