(See also Overview of Kidney Filtering Disorders.)
Small amounts of protein excreted in the urine (proteinuria) or blood excreted in the urine (hematuria) are sometimes discovered in people without symptoms when urine tests are done for some routine purpose. The presence of clumps of red blood cells (red blood cell casts) or abnormally shaped red blood cells is a clue for doctors that the blood in the urine came from glomeruli. Casts and proteinuria may be present because the person is recovering from a recent undiagnosed episode of kidney inflammation (nephritis). If this situation seems likely, a doctor needs only to recheck the person over the next weeks or months to make sure that the abnormalities resolve.
If red blood cells (particularly casts) and proteinuria persist, the cause is usually one of three disorders:
Immunoglobulin A (IgA) nephropathy, a type of glomerulonephritis caused by deposition of immune complexes (combinations of antibodies and antigens) in the kidneys that can be very mild and nonprogressive or become a severe disease leading to kidney failure (loss of most kidney function).
Hereditary nephritis (Alport syndrome), a progressive disorder that can be severe and lead to kidney failure and decreased hearing and vision.
Thin basement membrane disease (benign familial hematuria), a hereditary disorder caused by thinning of a part of the glomerulus called the basement membrane.
Thin basement membrane disease tends to cause red blood cells in the urine, but causes excretion of smaller amounts of protein than IgA nephropathy or hereditary nephritis and may not cause excretion of red blood cell casts. This disorder follows a mild and nonprogressive course. The diagnosis can usually be made with a kidney biopsy. However, a kidney biopsy is rarely done because the likelihood of finding a treatable disease is very low.
Doctors usually recommend that people with asymptomatic proteinuria and hematuria have a physical examination and undergo urine testing once or twice a year. Additional tests are done if the amount of protein or blood increases much, or if symptoms occur that suggest the development of a specific disease. Most people with asymptomatic proteinuria and hematuria syndrome do not worsen, and the condition may persist indefinitely.
American Kidney Fund, Proteinuria: Information and infographics on protein in the urine, including the connection between this symptom and chronic kidney disease
American Kidney Fund, IgA Nephropathy: General information on IgA nephropathy, including answers to frequently asked questions
American Kidney Fund, Hematuria: Information on blood in the urine, including the connection between this symptom and serious kidney disease