Urine Protein and Urine Protein to Creatinine Ratio

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.

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).

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:

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

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

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.

There are urine dipstick kits available that allow people to monitor the protein in their urine. This is usually not necessary, though, unless your healthcare provider is monitoring a known kidney condition.