Protein in urine — known as proteinuria (pro-tee-NU-ree-uh) — is excess protein found in a urine sample. Protein is one of the substances identified during a test to analyze the content of your urine (urinalysis).

Low levels of protein in urine are normal. Temporarily high levels of protein in urine aren't unusual either, particularly in younger people after exercise or during an illness.

Persistently high levels of protein in urine may be a sign of kidney disease.

Your kidneys filter waste products from your blood while retaining what your body needs — including proteins. However, some diseases and conditions allow proteins to pass through the filters of your kidneys, causing protein in urine.

Conditions that can cause a temporary rise in the levels of protein in urine, but don't necessarily indicate kidney damage, include:

• Dehydration
• Emotional stress
• Exposure to extreme cold
• Fever
• Strenuous exercise

Diseases and conditions that can cause persistently elevated levels of protein in urine, which might indicate kidney disease, include:

• Amyloidosis (buildup of abnormal proteins in your organs)
• Certain drugs, such as nonsteroidal anti-inflammatory drugs
• Chronic kidney disease
• Diabetes
• Endocarditis (an infection of the inner lining of the heart)
• Focal segmental glomerulosclerosis (FSGS)
• Glomerulonephritis (inflammation in the kidney cells that filter waste from the blood)
• Heart disease
• Heart failure
• High blood pressure (hypertension)
• Hodgkin's lymphoma (Hodgkin's disease)
• IgA nephropathy (Berger's disease) (kidney inflammation resulting from a buildup of the antibody immunoglobulin A)
• Kidney infection (pyelonephritis)
• Lupus
• Malaria
• Multiple myeloma
• Nephrotic syndrome (damage to small filtering blood vessels in the kidneys)
• Orthostatic proteinuria (urine protein level rises when in an upright position)
• Preeclampsia
• Pregnancy
• Rheumatoid arthritis (inflammatory joint disease)
• Sarcoidosis (collections of inflammatory cells in the body)
• Sickle cell anemia

If a urine test reveals protein in your urine, ask your doctor whether you need further testing. Because protein in urine can be temporary, your doctor might recommend a repeat test first thing in the morning or a few days later.

Your doctor might order other tests, such as a 24-hour urine collection, to determine if there is a cause for concern.

If you have diabetes, your doctor may check for small amounts of protein in urine — also known as microalbuminuria (my-kroh-al-byoo-min-U-ree-uh) — once or twice each year. Newly developing or increasing amounts of protein in your urine may be the earliest sign of diabetic kidney damage.