What is being tested?
The protein urine test measures the amount of protein being excreted in the urine. Elevated levels may be seen temporarily with conditions such as infections, stress, pregnancy, diet, cold exposure, or heavy exercise. Persistent protein in the urine suggests possible kidney damage or some other condition that requires additional testing to determine the caue.
There are several different kinds of protein urine tests. A semi-quantitative protein ‘dipstick’ is frequently performed as part of a urinalysis, generally on a random urine sample. The quantity of protein in a 24-hour urine sample may be measured and reported as the amount of protein excreted per 24 hours. Also, the amount of protein in a random urine sample may be measured and reported as the ratio of protein to creatinine (UPCR).
Creatinine, a by-product of muscle metabolism, is normally excreted into the urine at a constant rate. When a creatinine measurement is performed with a random protein urine test, the resulting protein/creatinine ratio can be used instead of the 24-hour protein urine test. Since saving all of the urine for a 24-hour period can be cumbersome for adults and difficult for infants and children, a random urine protein to creatinine ratio may sometimes be substituted for a 24-hour protein urine sample.
Proteins are essential for all living beings. Albumin, a protein produced by the liver, makes up about 60% of the protein in the blood. The rest is a mixture of globulins, including immunoglobulins. Proteins usually are not found in the urine. The kidneys (two organs found in the back at the bottom of the rib cage) filter the blood, removing waste and excreting it out of the body in the form of urine. When the kidneys are functioning normally, they retain or reabsorb filtered protein molecules and return them to the blood. If the kidneys are damaged or compromised due to other conditions, they become less effective at filtering causing detectable amounts of protein to spill over into the urine. Often, it is the smaller albumin molecules that are detected first. If the damage continues, the amount of protein in the urine increases, and globulins may also begin to be lost.
Proteinuria (protein in the urine) is frequently seen in chronic diseases, such as diabetes and hypertension (high blood pressure), with increasing amounts of protein in the urine reflecting increasing kidney damage. With early kidney damage, the patient often has no symptoms. As damage progresses or if protein loss is severe, the patient may have symptoms such as swelling and fluid retention (oedema), shortness of breath, nausea and fatigue. Excess protein production, seen with multiple myeloma, lymphoma and amyloidosis can also lead to proteinuria.
The presence of albumin in the urine (albuminuria) has been shown to be a good indicator of kidney disease in patients with diabetes and with high blood pressure. Therefore, most of the time the doctor may test specifically for albumin, as opposed to total protein in the urine (see albumin creatinine ratio urine; microalbuminuria (UACR).
How is it used?
Protein urine tests are used to help assess and follow the health of the kidney, and to help detect and diagnose early kidney damage and disease. A dipstick protein urine test is frequently performed as part of a urinalysis. It is used to look for the presence of protein in the urine. If slight to moderate amounts of protein are detected, then another urinalysis and dipstick protein test may be performed at a later time to see if there is still protein in the urine or if it has fallen back to undetectable levels.
If there is a large amount of protein in the first sample and/or the protein persists in the second sample, then the doctor may request a further laboratory urine protein measurement as a follow-up test. Since the dipstick primarily measures albumin, the laboratory protein urine test may also be requested if a doctor suspects that proteins other than albumin are being released.
A protein to creatinine ratio may be requested on a random urine sample if a child shows evidence of significant and persistent protein in their urine on a dipstick urine test. Children (as well as adults) sometimes have some degree of transient proteinuria without apparent kidney dysfunction and may have a higher excretion of protein into their urine during the day than at night. The doctor may monitor their urine at intervals to see if the amount of proteinuria changes over time.
Either a 24-hour protein urine or a random protein to creatinine ratio may be requested to monitor a patient with known kidney disease and/or damage. A dipstick protein urine and/or a protein to creatinine ratio may be used to regularly screen patients when they are taking a medication that may affect their kidney function.
The protein urine test tells the doctor that protein is present in the urine, but it does not indicate which types of protein are present or the cause of the proteinuria. When investigating the reason, the doctor may also request a serum and urine electrophoresis test to determine which proteins are being excreted and in what quantities. This is especially true if abnormal protein production is suspected, such as with multiple myeloma. The doctor may request further tests to look at urea and creatinine, albumin and total protein levels in the blood, which help evaluate kidney and liver function. If kidney disease or damage is suspected, imaging scans to evaluate the appearance of the organ may be requested.
When is it requested?
A dipstick protein urine test is measured whenever a urinalysis is performed. This may be done as part of a routine check-up, a pregnancy check-up, when a urinary tract infection is suspected, as part of a hospital admission, or whenever the doctor wants to evaluate kidney function. Repeat testing may also be done when a previous dipstick has been positive for protein to see if the protein excretion persists.
The laboratory random or 24-hour protein urine test may be requested as a follow-up test when the dipstick test shows that there is a large quantity of protein present in the urine and/or when protein is shown to be persistently present. Since the dipstick primarily measures albumin, the doctor may request a laboratory protein urine test even when there is little protein detected on the dipstick if they suspects there may be proteins other than albumin being released.
When a doctor is diagnosing the cause of proteinuria they also may request a urine electrophoresis test to determine exactly which proteins are being excreted and in what quantities. A serum electrophoresis also may be used to look at the proteins in the blood, especially if abnormal protein production is suspected. Other blood tests, such as a urea and creatinine, may be used to evaluate kidney function and albumin and/or total protein may be used to look at the proteins in the blood.
A protein to creatinine ratio may be requested on a random urine sample when a child shows evidence of significant and persistent protein in their urine on a dipstick test. It may also be requested when a patient has known kidney disease and/or damage and the doctor wants to monitor kidney function over time. A dipstick urine protein and/or a protein to creatinine ratio on a random urine sample may be used as a screen for kidney involvement when a patient is receiving treatment that may potentially affect kidney function.
What does the result mean?
A negative test result means that there is no detectable amount of protein in the urine at the time of testing.
Protein in the urine is a warning sign. It may indicate kidney damage or disease or be a transient elevation due to an infection, medication, vigorous exercise, diet, cold exposure, emotional or physical stress. Testing should be repeated after these conditions have resolved. In some people, it may be present during the day and absent at night when the patient is lying down. Leak of protein into the urine on standing which disappears on lying down (orthostatic proteinuria) is commonly seen particularly with increasing age and it carries no health risk. In pregnant women, elevated urine protein levels can be associated with pre-eclampsia.
When kidney damage is present, the amount of protein present is generally associated with the severity of damage, and increasing amounts of protein over time indicate increasing damage and decreasing kidney function. Proteinuria is associated with many diseases and conditions, including:
Is there anything else I should know?
The different methods of detecting protein in the urine vary in performance. For example, a positive dipstick protein test may be elevated due to other sources of protein, such as blood, semen or vaginal secretions in the urine. Since it measures primarily albumin, the dipstick occasionally may be normal when significant quantities of other proteins are present in the urine. A 24-hour urine sample gives the protein excretion rate over 24 hours and is considered the gold standard for measurement of urine protein. It will be accurate only if all of the urine is collected. A random laboratory protein to creatinine ratio, especially on a first morning voided urine, has become an accepted alternative method of measurement.
Common questions
Potentially yes. There are dipsticks available that allow patients to monitor the protein in their urine. This is usually not necessary unless your doctor is monitoring a known kidney condition.
This will depend on the reason for the damage. The goal is to detect kidney disease and damage early to minimise the damage and prolong kidney function. If the proteinuria detected is due to a kidney infection or urinary tract infection, the kidneys frequently will return to normal as the infection resolves. If it is due to a medication, then in most cases the kidneys are likely to return to normal or near normal function when the medication is stopped.
This is something to discuss with your doctor. If you have severe protein deficiency, that may need to be addressed, but ingesting additional protein also puts additional stress on your kidneys.
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