Glomerulonephritis is an injury to the kidney filters that cause blood to leak from the filters into the urine. The filters are called glomeruli (Latin) and nephritis is Greek for kidney inflammation, so this injury is called glomerulonephritis. This disease is often "silent" so many times you won't feel sick. The cause of this injury is not entirely known, but one kind of glomerulonephritis where the cause is known is related to strep infections such as strep throat. Other kinds of germs besides strep can cause this kind of kidney reaction. It's also possible no obvious infection was noticed, but this type of nephritis might be suspected anyway. If the infection related type is unlikely, other types need to be considered.
When the cause of glomerulonephritis is related to strep infections like strep throat, the infection itself is not in the kidneys. What happens is the filters react to things in the blood from the immune system defending against the infection. This doesn't occur in everyone. If the kidneys do react, blood from the filters tum the urine a rusty brown color for about two weeks after the strep infection, even if you were treated for strep. Since it occurs after a strep infection, it is called post strep glomerulonephritis. Approximately 95% of cases will improve without treating the kidney, but there may be a need to treat related problems such as high blood pressure. Often your doctor can take care of this type of nephritis with the advice of a pediatric kidney specialist called a pediatric nephrologist. Your doctor may refer you to a nephrologist, especially if another type of nephritis is suspected.
Other types of glomerulonephritis have no known cause. Membranoproliferative glomerulonephritis is one. It can cause permanent damage to the kidney filters, decreasing kidney function in over 50 % of cases, so it is important to identify it so it can be treated. There are blood tests that suggest the diagnosis, but the only way to diagnose it for sure is to take a tiny piece of the kidney (biopsy) and look at it with a microscope.
Another is called IgA Nephropathy. If you notice the blood in your urine comes and goes, especially at times when you have a cold or another infection, it may be IgA nephropathy. About 80% of this type of sickness can get better without treatment, but 20% of children with this problem may have kidney damage. If your case is mild, it can be followed as likely IgA, since treatment is not suggested for mild cases. A biopsy is the only way to get the exact diagnosis and find out the degree of injury to the glomeruli to see if treatment should be tried.
Nephritis can be part of diseases that affect other parts of the body. Systemic Lupus Erythematosus (SLE) is one. A disease called Henoch-Schonlein Purpura (HSP) is another that can cause serious nephritis in about 20% of cases. Proven treatments are not available for every kind of nephritis. Efforts are made to treat severe cases because losing kidney function is serious. Nephrologists have the experience to suggest treatments that have been shown to help.