What causes protein in urine?
Protein in the urine has many possible causes, some temporary and harmless, others worth treating early. Here’s how to tell them apart.
The most common causes
By far the two leading causes of persistent protein in the urine are:
- Diabetes. High blood sugar over time damages the kidneys’ filters, and leaking protein is often the first measurable sign of diabetic kidney disease.
- High blood pressure. Elevated pressure injures the small blood vessels in the kidneys, allowing protein to escape into the urine. Learn more about how blood pressure damages the kidneys.
Together, diabetes and high blood pressure account for the large majority of chronic kidney disease, so they’re always the first things doctors check for.
Temporary, usually harmless causes
Protein can appear briefly and then clear on its own after:
- Strenuous exercise
- Fever or a recent illness
- A urinary tract infection
- Dehydration
- Standing upright for long periods (a benign pattern called orthostatic proteinuria, most common in younger people)
Because these are transient, a single positive test is normally repeated before any conclusions are drawn.
Less common but important causes
Sometimes proteinuria points to a specific kidney condition, such as a disease of the filters themselves (glomerular diseases like IgA nephropathy or focal segmental glomerulosclerosis), lupus affecting the kidneys, or other inflammatory or inherited conditions. Heavy protein loss can also be part of a pattern called nephrotic syndrome, which may cause swelling in the legs and around the eyes.
How the cause is sorted out
To find the source, your doctor will confirm the protein is persistent, measure your kidney function, review your blood pressure and blood sugar, and sometimes order additional blood or urine tests. If the cause isn’t clear or the protein level is high, a nephrologist can dig deeper (occasionally with a kidney biopsy) and tailor treatment to the specific cause.
This article is for general education and is not a substitute for personalized medical advice. Talk with your doctor or nephrologist about your specific situation.