Protein in urine — also called proteinuria (pro-tee-NU-ree-uh) — is an excess of bloodborne proteins in urine. Protein is one of the substances measured in a lab test to analyze the contents of urine (urinalysis).

The term "proteinuria" is sometimes used interchangeably with the term "albuminuria," but these terms have somewhat different meanings. Albumin (al-BYOO-min) is the most common type of protein circulating in blood. Some urine tests only detect an excess of albumin in urine. Excess albumin in urine is called albuminuria (al-BYOO-mih-NU-ree-uh). Proteinuria refers to an excess of multiple blood proteins in urine.

Low levels of protein in urine are typical. 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 keeping 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 (when the body doesn't have enough water and other fluids to work as it should)
• Exposure to extreme cold
• Fever
• Strenuous exercise

Tests to identify protein in urine are critical for diagnosing and screening for diseases of the kidneys or other conditions affecting kidney function. These tests are also used to monitor disease progression and treatment effect. These diseases and conditions include:

• Chronic kidney disease
• Diabetic nephropathy (kidney disease)
• Focal segmental glomerulosclerosis (FSGS)
• Glomerulonephritis (inflammation in the kidney cells that filter waste from the blood)
• High blood pressure (hypertension)
• IgA nephropathy (Berger disease) (kidney inflammation resulting from a buildup of the antibody immunoglobulin A)
• Lupus
• Membranous nephropathy
• Multiple myeloma
• Nephrotic syndrome (damage to small filtering blood vessels in the kidneys)
• Preeclampsia

Other conditions and factors affecting the kidneys that may result in protein in urine include:

• Amyloidosis (buildup of abnormal proteins in your organs)
• Certain drugs, such as nonsteroidal anti-inflammatory drugs
• Heart disease
• Heart failure
• Hodgkin lymphoma (Hodgkin disease)
• Kidney infection (also called pyelonephritis)
• Malaria
• Orthostatic proteinuria (urine protein level rises when in an upright position)
• Rheumatoid arthritis

If a urine test reveals protein in your urine, your health care provider may ask you to have more testing done. Because protein in urine can be temporary, you may need to repeat a urine test first thing in the morning or a few days later. You also may need to do a 24-hour urine collection for lab testing.

If you have diabetes, your doctor may check for small amounts of protein in urine — also known as microalbuminuria (my-kroh-al-BYOO-mih-NU-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.