Your kidneys continuously filter your blood, excreting waste products while holding back proteins and other important molecules. Healthy kidneys normally allow almost no protein to be lost in the urine. Although protein in the urine, or proteinuria, is an important marker of disease, there are benign causes of proteinuria, as well.
Testing for Urine Protein
If your kidneys are functioning normally, you should have almost no detectable protein in your urine. Several common laboratory tests are used to check for proteinuria, including urine dipsticks for quick screening purposes, automated instruments for a more sensitive measurement of total protein and 24 hour urine collections to look for protein loss over time. Although results can vary somewhat between different laboratories, the amount of protein in a random sample of urine is normally less than 8 mg/dL and for a 24-hour collection, less than 150 mg total, according to MedlinePlus.
Increased Protein in Urine
Increased urine protein levels are a non-specific finding seen with a wide variety of medical conditions, ranging from totally harmless to potentially life-threatening. Common causes for proteinuria include kidney disease, high blood pressure, diabetes, drugs, infections and tumors such as multiple myeloma. Increased amounts of protein in the urine are never considered normal. However, mild proteinuria doesn't always indicate a serious disorder. Additional testing and evaluation by your health-care provider is necessary to make this determination.
Benign Causes of Proteinuria
Several conditions cause protein to appear in your urine without indicating a serious problem. A variety of medications can interfere with accurate protein measurements, including many common antibiotics, lithium, salicylates or any drug that damages the kidneys. A temporary increase in your urine protein level commonly occurs with fever, strenuous exercise, exposure to extreme cold, congestive heart failure and seizures, but returns to normal shortly afterwards, according to "Essentials of Nephrology." A condition known as idiopathic transient proteinuria is occasionally seen in children and young adults, in which a high urine protein is found in a urine sample but is gone on later testing. Orthostatic proteinuria also occurs in young adults, characterized by protein appearing in the urine when the person is up and walking during the day, but not found in urine from overnight while lying down. This condition usually disappears by age 30.
Approach to Proteinuria
Proteinuria serves as an important marker for many serious diseases, so a finding of protein in your urine needs further medical evaluation. Your health care provider will normally perform a complete history and physical exam, review all your laboratory results and order further testing as needed to reach a diagnosis. Keep in mind that not every case of proteinuria indicates a serious problem, and a mild elevation in protein might simply reflect your body's normal reaction to a temporary illness or other benign situation, especially if you are otherwise young and healthy.
- Lab Tests Online: Urine Protein and Urine Protein to Creatinine Ratio
- MedlinePlus: Protein-urine
- "Essentials of Nephrology, Second Edition"; R. Kasi Visweswaran, Editor; 2009