Rudi Hayden

Urologist

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Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

Urine Protein


At a Glance

Why Get Tested?

To screen for excess protein in the urine, to help evaluate and monitor kidney function, and to detect kidney damage

When to Get Tested?

As part of a routine physical, as a follow-up to a previous positive urine protein test, or when you have a disorder or disease that affects the kidney

Sample Required?

A single urine sample collected at any time (random) or 24-hour urine sample; occasionally, a split 24-hour sample, with the night collection (11pm to 7am) separated from the day collection (7am to 11pm). Often, a blood sample may also be taken to measure your creatinine and serum protein levels, especially when a 24-hour urine has been ordered.

Test Preparation Needed?

None

The Test Sample

What is being tested?

Urine samplesUrine protein tests detect and/or measure protein being released into the urine. Normal urine protein elimination is less than 150 mg/day and less than 30 mg of albumin/day. 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 cause.

There are several different kinds of urine protein tests, including:

  • A semi-quantitative protein "dipstick" may be 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 released per 24 hours.  
  • The amount of protein in a random urine sample may be measured along with urine creatinine and reported as the ratio of urine protein to creatinine (UPCR). 

Creatinine, a byproduct of muscle metabolism, is normally released into the urine at a constant rate. When both a urine creatinine and a random urine protein test are performed, the resulting protein/creatinine ratio approaches the accuracy of the 24-hour urine protein 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 is sometimes substituted for a 24-hour urine protein sample.

Plasma proteins are essential for all living beings. The kidneys, two organs found in the back at the bottom of the rib cage, recapture these proteins by filtering the blood by removing wastes and eliminating them from the body in the urine. When the kidneys are functioning normally, they retain or reabsorb the filtered proteins and return them to the blood.

However, if the kidneys are damaged or compromised due to other conditions, they become less effective at filtering, causing detectible amounts of protein to spill over into the urine. Routine dipstick testing of urine measures the presence of albumin. Albumin, a protein produced by the liver, makes up about 50%-60% of the protein in the blood. The rest is a mixture of globulins, including immunoglobulins. As kidney damage progresses, the amount of albumin in the urine increases, a key factor in the early detection of a potential kidney disorder.

Proteinuria is frequently seen in chronic diseases, such as diabetes and hypertension, with increasing amounts of protein in the urine reflecting increasing kidney damage. With early kidney damage, the affected person is often asymptomatic. As damage progresses, or if protein loss is severe, the person may develop symptoms such as edema, shortness of breath, nausea, and fatigue. Excess protein overproduction, as 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 sensitive indicator of kidney disease in people with diabetes and with hypertension. Therefore, it is recommended that people with these conditions be regularly screened for albumin in the urine, as opposed to total urine protein (see Urine Albumin).

How is the sample collected for testing?

A random urine sample is collected in a clean container. For a 24-hour urine collection, the collection process generally begins first thing in the morning by discarding the first morning void and then collecting all of the urine for the remaining 24-hour period. It is important that the sample be refrigerated during this time period. There should be no preservative in the container.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

Urine protein testing is used to detect protein in the urine (proteinuria). A semi-quanititative test such as a dipstick urine protein may be used to screen people for the presence of protein in the urine as part of a routine urinalysis.

A urine protein test is often used to screen for, help evaluate, and monitor kidney function and to help detect and diagnose early kidney damage and/or disease. However, the test can also help screen for several other conditions that can cause proteinuria.

If slight to moderate amounts of protein are detected, then a repeat urinalysis and dipstick protein may be performed at a later time to see if there is still protein in the urine or if it has become undetectable.

If there is a large amount of protein in the first sample, repeat testing will be ordered. If increased levels of urine protein are observed in follow-up specimens, then a 24-hour urine protein may be ordered along with certain blood tests. Since the dipstick method primarily measures the protein albumin, and if follow-up, repeat urine samples are positive, a 24-hour urine test also may be ordered to obtain more detailed information.

A urine protein to creatinine ratio (UP/CR) may be ordered on a random urine sample if there is evidence of significant and persistent protein in the urine. Children and sometimes adults occasionally have some degree of transient proteinuria without apparent kidney dysfunction and may release more protein into their urine during the day than at night. The healthcare practitioner may monitor their urine at intervals to see if the amount of proteinuria changes over time.

Either a 24-hour urine protein or a random protein to creatinine ratio may be used to monitor a person with known kidney disease or damage. A dipstick urine protein and/or a protein to creatinine ratio may be used to screen people on a regular basis when they are taking a medication that may affect their kidney function.

A positive urine protein test tells a healthcare practitioner that protein is present in the urine, but it does not indicate which types are present or the cause of the proteinuria. When investigating the reason, a healthcare practitioner may order additional laboratory tests, such as:

  • Comprehensive metabolic panel (CMP)—includes tests such as BUN, creatinine, albumin and total protein, which help evaluate kidney and liver function
  • A full urinalysis—if a condition such as urinary tract infection is also suspected
  • Serum and urine protein electrophoresis test—to determine which proteins are being released into the urine and in what quantities; this is especially true if the healthcare practitioner suspects abnormal monoclonal protein production, such as with multiple myeloma or lymphoma.

See the article on Proteinuria for more on follow-up tests.

If kidney disease or damage is suspected, the healthcare practitioner may also order imaging scans (ultrasonography or CT scan) to evaluate the appearance of the organ.

When is it ordered?

A dipstick urine protein is measured frequently as a screening test whenever a urinalysis is performed. This may be done as part of a routine physical, a pregnancy workup, when a urinary tract infection is suspected, as part of a hospital admission, or whenever a healthcare practitioner 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 persists.

A 24-hour urine protein may be ordered as a follow-up test when the dipstick test shows that there is a large quantity of protein present in the urine or when protein is shown to be persistently present. Since the dipstick primarily measures albumin, the healthcare practitioner may order a 24-hour urine protein test even when there is little protein detected on the dipstick if the practitioner suspects that there may be proteins other than albumin being released.

A protein to creatinine ratio may be ordered on a random urine sample when a child shows evidence of significant and persistent protein in his or her urine with the dipstick urine test.

Urine protein testing may be ordered on a regular basis when someone is taking a medication that may potentially affect kidney function, including certain antibiotics, analgesics, COX-2 inhibitors (some non-steroidal anti-inflammatory drugs), and proton pump inhibitors (gastric reflux).

What does the test result mean?

A negative test result means that there is no detectable amount of protein in the urine at the time of testing.

Protein detected in a random urine sample may be a transient elevation due to an infection, medication, vigorous exercise, pregnancy, diet, cold exposure, or emotional or physical stress. Testing should be repeated after these conditions have resolved.

Protein in the urine may also be a warning sign of a serious condition. Typically, three positive urine samples over a period of time without other significant symptoms will often be followed up with additional tests, including a 24-hour urine.

Persistent and/or an increased amount of protein in the urine may indicate kidney damage or disease. With kidney disease, the amount of protein present is generally associated with the severity of damage. Increasing amounts of protein over time indicate increasing damage and decreasing kidney function.

Proteinuria may also be associated with many other diseases and conditions. A healthcare practitioner may order other tests and take into account those results to help determine the cause. Some examples of these causes include:

  • Amyloidosis
  • Bladder cancer
  • Congestive heart failure
  • Diabetes
  • Drug therapies that are potentially toxic to the kidneys
  • Goodpasture syndrome
  • Heavy metal poisoning
  • Hypertension
  • Multiple myeloma
  • Pre-eclampsia in pregnant women
  • Lupus
  • Urinary tract infection

For more details, select the links from the list above or read the article on Proteinuria.

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 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 may occasionally be normal when significant quantities of other proteins are present in the urine.

A 24-hour urine sample gives the protein elimination rate over 24 hours. It will be accurate only if all of the urine is collected. The protein to 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 elevated, then protein is present; if it is negative, it is possible that the person was just not releasing measurable amounts of protein at that time.