Proteinuria is a defined by the presence of protein in the urine. If proteinuria occurs the most common protein to leak from the blood into the urine is albumin due to its small size. Albuminuria refers to albumin in the urine and is often used interchangeably with proteinuria. Albuminuria is a very sensitive indicator of damage and scarring within the delicate filtering capillaries of the kidneys known as glomeruli. Proteinuria is without symptoms and may be a sign of silent kidney disease or damage. Although a variety of diseases or conditions may be associated with proteinuria, most commonly hypertension (high blood pressure) (see Dr Sweeney’s article on hypertension) or diabetes mellitus (high blood sugar) are causes of albuminuria. It is now know that albuminuria in these conditions is strongly associated with vascular disease especially relating to the cardiovascular system. Early detection of albuminuria may be important in initiating early treatment with certain blood pressure medications or dietary therapy. Inflammation within glomeruli (glomerulonephritis) may be another reason for proteinuria.
The amount of protein in the urine reflects the degree of damage occurring within the glomeruli. When the albuminuria is greater than 3000 milligrams it is termed nephrotic syndrome and is often associated with swelling in the legs or face, foamy urine, and high cholesterol levels. The higher the amount of albuminuria, the more likely that permanent damage may be present in the glomeruli as reflected by a decrease in the filtering ability of the kidneys. A marker of the kidney’s filtering ability is the creatinine level in the blood and this may increase as kidney function worsens.
A simple urinalysis can only show the degree of proteinuria and not the exact amount. A 24 hour urine collection may be necessary to measure the actual proteinuria over the 24 hour period. Albumin level in the blood may be decreased as albuminuria worsens. In diabetes mellitus the presence of microalbuminuria is a sensitive indicator of cardiovascular damage. Microalbuminuria means albumin levels undetectable on a dipstick urinalysis but is detectable on a special sensitive urine test. Patients with diabetes mellitus will typically have a microalbumin urine test done at the time of diagnosis and yearly thereafter.
The treatment of proteinuria will depend upon the cause of proteinuria and whether there is hypertension or not. High blood pressure (greater then 140/85) will worsen proteinuria and kidney function over time. The optimal blood pressure would be in less than 130/80 with the use of preferably an angiotensin converting enzyme inhibitor (ACEI) or angiotension receptor blocker (ARB). The addition of other blood pressure meds may worsen or improve proteinuria so it is important to have a complete assessment of meds by a qualified physician. In diabetes mellitus, excellent control of blood sugars will stabilize proteinuria. Low protein diets also are beneficial for proteinuria. The long term goal of therapy is to maintain excellent blood pressure control while decreasing proteinuria and maintaining it at a very low level.
Nephrotic syndrome caused by inflammation of glomeruli may sometimes be treated with immune suppressing medications including prednisone (steroid) and/or stronger immune suppressive medications (cyclophosphamide) which may have significant side effects. Usually a kidney biopsy may be necessary to diagnose the cause of nephrotic syndrome unless it is caused by diabetes mellitus. ACEI or ARBs may be used to decrease proteinuria. A diuretic (water pill) may be necessary to remove excess swelling.
Obesity or significantly being overweight may also result in proteinuria. There may be hormonal effects that promote proteinuria in obesity in particular excess insulin production due to insulin resistance of fatty tissue. Sustained weight loss may reduce proteinuria and provide general health benefits as well.
Mild proteinuria by be present in children or young adolescents as they undergo active growth. This is termed orthostatic proteinuria and is benign and harmless.
In summary, proteinuria is a common reason for referral to a Nephrologist and is usually discovered on a routine urinalysis. Albuminuria is the most common form of proteinuria. It will prompt additional blood and urine testing and possibly a kidney ultrasound. The most common reasons for albuminuria include hypertension, diabetes mellitus, and obesity. Albuminuria is a sensitive indicator of vascular or circulatory damage when present with these medical conditions. More severe degrees of proteinuria may reflect more serious damage to kidney filtering areas and may warrant a kidney biopsy, more extensive blood and urine testing, and stronger medications for treatment. All patients with hypertension or diabetes mellitus should have a urinalysis done as part of their initial evaluation and repeated on a yearly basis along with a test for microalbuminuria.
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