Protein in Urine as a Marker of Disease
The kidneys act as filtration units for the blood. As blood passes through the kidneys, they filter out waste, leaving behind essential molecules which then recirculate through the body.
Most proteins are too large to filter through into the urine; hence in a healthy person protein is not present in urine. However, if the kidneys are damaged, proteins are able to filter through into urine. The protein most commonly found in urine is albumin, which is found in the blood, and helps to retain fluids.
In a healthy metabolic state, urine sometimes contains trace amounts of protein. For example, this can happen after a strenuous physical workout. Other factors such as extreme temperatures, fever, and emotional stress can temporarily increase protein levels in urine by a small ammount. However, significant amounts of protein in the urine over the long-term can indicate that something is wrong.
When the kidneys become damaged—typically through some sort of inflammation—the resulting symptoms often include protein in urine. Many infections and diseases can cause this type of inflammation to occur, including hypertension, diabetes, and kidney disease.
The presence of protein in urine is, therefore, a signal that the kidneys have been sufficiently damaged by inflammation to allow larger molecules to pass into the urine.