Urine protein

What is being measured?
The urine protein test measures the amount of protein passed in the urine. There are several types of urine protein test. A semi-quantitative dipstick test for protein may be carried out as part of a urinalysis, usually on a random urine sample. The amount of protein in a 24-hour urine sample can be measured and reported as the amount of protein passed in 24 hours. In addition, the amount of protein in a random urine sample can be measured and reported as a ratio of protein to creatinine. As collecting urine for 24 hours can be inconvenient for adults and difficult for babies and children, a urine protein/creatinine ratio on a random sample can sometimes replace a 24-hour sample. Creatinine, a product of muscle metabolism, is normally passed in the urine at a steady rate. When creatinine is measured together with urine protein on a random sample, the protein/creatinine ratio comes close to the accuracy of a 24-hour urine protein test.

Albumin, a protein made by the liver, makes up about 60% of the protein in the blood. The rest is a mixture of globulins, including immunoglobulins. Protein is not normally found in the urine. The kidneys (two organs located in the back, at the bottom of the rib cage) filter the blood, removing waste and eliminating it from the body as urine. When the kidneys are working normally, they can retain or reabsorb filtered proteins and return them to the circulation. If the kidneys are damaged, however, they filter less effectively and small amounts of protein start to pass into the urine. Albumin, one of the smaller protein molecules, is often the first to be detected. If the damage persists, the amount of protein in the urine increases, and globulins also start to be lost.

Proteinuria (protein in the urine) is frequently seen in chronic diseases such as diabetes and high blood pressure, with the amount of protein increasing as kidney damage increases. With early kidney damage, the patient often has no symptoms. As the damage increases, or if protein loss is severe, the patient may have symptoms such as oedema (swelling and fluid retention), shortness of breath, nausea and tiredness. Excessive protein production, as seen in multiple myeloma, can also lead to proteinuria.

Albumin in the urine (albuminuria) has been shown to be a sensitive indicator of kidney disease in patients with diabetes and high blood pressure. For this reason, in some situations the doctor may test specifically for albumin, rather than total protein, in the urine (see microalbuminuria).

How is the sample collected for testing?
A random urine sample is collected in a clean container. For a 24-hour collection, all urine must be collected over a 24-hour period. It is important for the sample to be kept refrigerated during this period. There should be no preservatives in the container.

How is it used?
When is it requested?
How is the test interpreted?
What else should I know?

How is it used?
The urine protein test is used to detect protein in the urine, to help evaluate and monitor kidney function, and to help detect and diagnose early kidney damage and kidney disease. Dipstick urine protein is performed routinely as part of a urinalysis and is used to screen the population for urine protein. If a mild to moderate amount of protein is detected, another urinalysis and dipstick protein test may be carried out later to see whether protein is still present in the urine or has returned to an undetectable level. If there is a large amount of protein in the first sample and/or it persists in the second sample, the doctor may request a 24-hour urine test as a follow-up. Because the dipstick test mainly measures albumin, a 24-hour protein test may also be requested if the doctor suspects that proteins other than albumin are being lost.

The urine protein test tells the doctor that protein is present in the urine, but it does not show which type is present or what is causing the proteinuria. When investigating further, the doctor may also request serum and urine electrophoresis to determine which proteins are being lost and in what amounts. This is especially true if abnormal protein production is suspected, as in multiple myeloma. The doctor may request a comprehensive metabolic panel (CMP) to see the levels of albumin and total protein in the blood and to help evaluate kidney and liver function. If kidney disease or damage is suspected, an imaging scan may also be requested to assess the appearance of the organ.

A random urine protein/creatinine ratio may be requested if a child shows persistent, significant evidence of protein in the urine on a dipstick test. Children (like adults) sometimes have temporary proteinuria without any apparent kidney dysfunction and may lose significant amounts of protein in the urine both during the day and at night. The doctor may monitor the urine at intervals to see whether the level of proteinuria changes over time.

Both 24-hour urine protein and a random urine protein/creatinine ratio may be requested to monitor a patient with known kidney disease or damage. Dipstick urine protein or a protein/creatinine ratio may be used to check patients regularly when they are taking medicines that can affect kidney function.

When is it requested?
Dipstick urine protein is frequently measured as a screening test when a urinalysis is carried out. This may be done as part of a medical check-up, when preparing for pregnancy, when a urinary tract infection is suspected, as part of a hospital admission, or when the doctor wants to assess kidney function. It may also be done when a previous dipstick test was positive for protein, to see whether protein loss is continuing.

A 24-hour urine protein test may be requested as a follow-up test when a dipstick test shows a high level of protein in the urine and/or when protein is persistently present. Because the dipstick test mainly measures albumin, the doctor may also request a 24-hour urine protein test when the dipstick detects only a small amount, if they suspect that proteins other than albumin may be being lost.

When the doctor is investigating the cause of proteinuria, they may also request urine electrophoresis to determine exactly which proteins are being lost and in what amounts. Serum electrophoresis may also be requested to look at the proteins in the blood, especially if abnormal protein production is suspected. Other blood tests, such as BUN (urea) and creatinine, may be requested to assess kidney function, and albumin and/or total protein tests may be carried out to look at the proteins in the blood.

A random urine protein/creatinine ratio may be requested when a child shows evidence of significant, persistent proteinuria on a dipstick test. It may also be requested when a patient has known kidney disease or damage and the doctor wants to monitor kidney function over time. Dipstick urine protein and/or a random urine protein/creatinine ratio may be used to check for kidney involvement when a patient is taking medicines that could affect kidney function.

How is the test interpreted?
Proteinuria is a warning sign. It may indicate kidney damage or disease, or it may be a temporary increase due to infection, medicines, exercise, or emotional or physical stress. In some people it may be present during the day and absent at night when the person is lying down (orthostatic proteinuria). In pregnant women, a high level of protein in the urine may be associated with pre-eclampsia.

When kidney damage is present, the protein level is generally related to the severity of the damage, and a level that increases over time indicates increasing damage and declining kidney function. Proteinuria is associated with many diseases, including:

• Amyloidosis
• Bladder cancer
• Congestive heart failure
• Diabetes
• Drug treatments that are potentially toxic to the kidneys
• Glomerulonephritis
• Goodpasture syndrome
• Heavy metal poisoning
• High blood pressure
• Kidney infection
• Multiple myeloma
• Polycystic kidney disease
• Systemic lupus erythematosus
• Urinary tract infection

What else should I know?
The different methods for detecting protein in the urine vary in how they perform. For example, a positive dipstick protein may be raised because of other sources of protein in the urine, such as blood, semen or vaginal secretions.

Because it mainly measures albumin, the dipstick may occasionally be normal when significant amounts of other proteins are present in the urine. A 24-hour urine sample represents protein excretion over 24 hours; it will only be accurate if all the urine is collected. The protein/creatinine ratio is more of a snapshot of how much protein is in the urine at the time the sample is collected. If it is raised, protein is present; if it is negative, it is possible that the patient was simply not losing a measurable amount of protein at that moment.

1. Can urine protein be tested at home?
2. Can kidney damage be reversed?
3. Should I eat more protein to avoid losing protein?

1. Can urine protein be tested at home?
Potentially, yes. Dipsticks are available that allow patients to monitor protein in their urine. This is not usually necessary, however, unless the doctor is monitoring known kidney disease.

2. Can kidney damage be reversed?
Generally, no. The aim is to detect kidney disease and damage early in order to minimise the damage and preserve kidney function for longer. If the proteinuria detected is due to a kidney infection or a urinary tract infection, the kidneys will usually return to normal once the infection clears. If it is due to drug treatment, in many cases the kidneys will probably return to normal (or near-normal) function when the treatment is stopped.

3. Should I eat more protein to avoid losing protein?
This is something to discuss with your doctor. If you have a severe protein deficiency, it will need to be corrected, but eating more protein puts additional strain on the kidneys.