Urine protein testing 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 disease. A semi-quanititative test such as a dipstick urine protein is used to screen the general population for the presence of protein in the urine as part of a routine urinalysis. 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 dropped 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 a 24-hour urine protein may be used as a follow-up test. Since the dipstick primarily measures albumin, the 24-hour urine protein test also may be ordered if a doctor suspects that proteins other than albumin are being released.
The urine protein test tells the doctor that protein is present in the urine, but it does not indicate which types are present or the cause of the proteinuria. When a doctor is investigating the reason, the doctor also may order a serum and urine protein electrophoresis test to determine which proteins are being excreted and in what quantities. This is especially true if he suspects abnormal protein production, such as with multiple myeloma. The doctor may order a Comprehensive Metabolic Panel (CMP) to look at albumin and total protein levels in the blood and to help evaluate kidney and liver function. If kidney disease or damage is suspected, the doctor may also order imaging scans to evaluate the appearance of the organ.
A protein to creatinine ratio may be ordered on a random urine sample if a child shows evidence of significant and persistent protein in their urine with the dipstick urine test. Children, and sometimes adults, occasionally 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 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 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 the doctor wants to evaluate kidney function. It may also be done when a previous dipstick has been positive for protein to see if the protein excretion 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 doctor may order a 24-hour urine protein test even when there is little protein detected on the dipstick if the doctor 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 their urine with the dipstick urine test. It may also be ordered when a person has known kidney disease 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 someone is taking a medication that may potentially affect kidney function.
Protein in the urine is a warning sign. It may indicate kidney damage or disease or it may be a transient elevation due to an infection, medication, vigorous 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, elevated urine protein levels can be associated with preeclampsia.
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:
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 excretion 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 excreting measurable amounts of protein at that time.
This article was last reviewed on December 6, 2012. | This article was last modified on February 24, 2015.
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