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The Test Sample
What is being tested?
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 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.
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.