Healthy kidneys prevent proteins in the blood stream from spilling into the urine. This is why doctors often first suspect kidney disease when a patient presents with elevated urine protein, or proteinuria. Proteinuria often occurs when the kidneys become inflamed or diseased. In a few rare instances, mild proteinuria can even be normal.
Controlling proteinuria is an important element of treatment because proteinuria itself can hasten the rate of renal failure independently of the underlying disease.
Kidney disease caused by diabetes is called diabetic nephropathy. The first symptom of diabetic nephropathy is often high urine protein. Diabetic patients should have their urine checked frequently because diabetic nephropathy is the leading cause of kidney failure in the United States. According to the National Institute of Diabetes, Digestive and Kidney Diseases, 43.8 percent of all renal failure was caused by diabetes in 2007.
Proteinuria is often the first symptom of glomerular disease. Glomerular disease is a broad category encompassing many different diseases that affect the glomeruli. These diseases include IgA nephropathy, focal segmental glomerularsclerosis (FSGS), membranoproliferative glomerular nephritis (MPGN), membranous nephropathy, IgM nephropathy and many others. Treatment of these diseases often focuses upon controlling proteinuria and other symptoms such as hypertension.
Pediatric kidney diseases
Children are more vulnerable to minimal change disease and post-streptococcal glomerular nephritis. The first symptom of both of these diseases is severe proteinuria. Although children can present multiple times with severe proteinuria due to minimal change disease, this condition usually resolves by adolescence.
Proteinuria due to post-streptococcal glomerular nephritis resolves quickly. In many instances, it is gone within several weeks.
Some kidney conditions are congenital. This means that the condition is present when the baby was born. Congenital diseases that produce proteinuria are polycystic kidney disease and Alport syndrome.
Birth defects involving the kidneys do not automatically cause proteinuria. For example, proteinuria is usually absent with renal hypoplasia, the most common congenital kidney defect.
Mild proteinuria can be completely normal. On the website UptoDate, Dr. Burton Rose writes that 2 to 5 percent of adolescents will have orthostatic or postural proteinuria. Proteinuria is described as orthostatic if the proteinuria goes away when the patient lies down.