What is Protein Creatinine Ratio - Urine?
Also Known As:
24-Hour Urine Protein, Urine Total Protein, Urine Protein to Creatinine Ratio, UPCR
Urine 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 24 hours 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.
Protein in the urine, also called proteinuria, is frequently seen in chronic diseases, such as diabetes and/or hypertension, with increasing amounts of protein in the urine reflecting increasing kidney damage. There are often no signs and symptoms with early kidney damage. As kidney damage progresses, or if protein loss is severe, you may develop symptoms such as fluid build-up (edema), shortness of breath, nausea, and fatigue. The production of too much protein, as seen with multiple myeloma, lymphoma, and amyloidosis, can also lead to proteinuria.
The presence of albumin in the urine (albuminuria) is a sensitive indicator of kidney disease in people with diabetes and/or 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 test used?
Urine protein testing is used to detect excess protein in the urine (proteinuria). A semi-quantitative test such as a dipstick urine protein may be used to screen for the presence of protein in the urine as part of a routine urinalysis.
A urine protein test may be 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.