The Test Sample
What is being tested?
Urine protein tests detect and/or measure protein being excreted in the urine. Proteins are not normally found in the urine but may be seen temporarily with conditions such as infections and stress. Persistent protein in the urine suggests possible kidney damage.
There are several different kinds of urine protein tests, including:
- A semi-quantitative protein "dipstick" that 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 excreted 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 excreted 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.
The kidneys, two organs found in the back at the bottom of the rib cage, filter the blood, removing wastes and excreting them out of the body in the form of urine. When the kidneys are functioning normally, they retain or reabsorb filtered proteins and return them to the blood. However, if the kidneys are damaged, they become less effective at filtering, and detectible amounts of protein begin to find their way into the urine. Often, it is small albumin molecules that are detected first. 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. As kidney damage progresses, the amount of albumin in the urine increases, and globulins may also begin to be lost.
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 production, such as may be seen with multiple myeloma, 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, in some situations the doctor may test specifically for albumin in the urine, as opposed to total urine protein (see Microalbumin).
How is the sample collected for testing?
A random urine sample is collected in a clean container. For a 24-hour urine collection, all of the urine is collected for a 24-hour period. It is important that the sample be refrigerated during this time period. There should be no preservative in the container.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.