Albuminuria also called proteinuria or urine albumin—is a condition in which urine contains an abnormal amount of protein. Albumin is the main protein in the blood. Proteins are the building blocks for all body parts, including muscles, bones, hair, and nails. Proteins in the blood also perform a number of important functions. They protect the body from infection, help blood clot, and keep the right amount of fluid circulating throughout the body.