Protein is a basic component of muscles, bones, hair and nails and is important for protection against infection, blood clotting and fluid balance regulation. Protein in urine is known as proteinuria or albuminuria. According to American Family Physicians, proteinuria is defined as greater than 150 mg of protein in the urine per day. When your kidneys function properly, they will filter wastes and water from blood, but not protein.
The kidneys are bean-shaped organs that sit on the left and right sides of your lower back. Inside each kidney are structures, called glomeruli, which filter blood. Your kidneys filter about 200 quarts of blood and produce about 2 quarts of waste each day, according to the National Kidney and Urologic Diseases Information Clearinghouse. This waste is excreted from the body as urine.
Trace to small amounts of protein in the urine can occur as a result of infection, drug toxicity or emotional or physical stress. Pregnant women may experience proteinuria as a result of preeclampsia. Large amounts of protein in urine, greater than 2 grams per day, is a sign of glomerular damage. Your urine may appear foamy or pink-tinged. You may also notice swelling, caused by edema, or fluid retention, in your hands and ankles.
Proteinuria is evaluated by assessing the amount and type of protein in the urine. According to Lab Tests Online, about 60 percent of protein in blood is albumin. Albumin is the smallest of the protein molecules. Larger protein molecules include globulins and immunoglobulins. Under normal circumstances, these molecules are too large to be filtered by the glomeruli into urine. Excessive protein in urine may be due to the presence of large protein molecules and should be evaluated by your physician.
An analysis of a random urine sample can detect small to moderate amounts of protein, but will not identify the type of protein or the cause. If protein is present, your doctor may order a repeat test for a later time and compare the results. If a repeat test detects protein, your doctor may have you collect a 24-hour urine sample, which will allow your doctor to identify the type of protein. Your doctor may order other tests to identify the cause of the proteinuria. A referral to a kidney specialist, or nephrologist, may be necessary when urine protein is greater than 2 grams per day.
- National Kidney and Urologic Diseases Information Clearinghouse; Proteinuria; March 2009
- Lab Tests Online: Urine Protein and Urine Protein to Creatinine Ratio
- National Kidney and Urologic Diseases Information Clearinghouse; Glomerular Diseases; April 2006
- American Academy of Family Physicians; Proteinuria in Adults: A Diagnostic Approach; September 2000