What is being tested?Protein is not normally found in the urine, and urine protein tests detect and/or measure protein being excreted in the urine. There are several different kinds of urine protein tests. 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 will be measured and reported as the amount of protein excreted per 24 hours. Also, 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.
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. Proteins are not normally found in the urine. 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 the smaller albumin molecules that are detected first. If the damage continues, the amount of protein 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 patient is often asymptomatic. As damage progresses, or if protein loss is severe, the patient may have 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 patients 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).
