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Post-Infectious Glomerulonephritis

October 15, 2010

A few years ago, a visiting speaker reported that post-streptococcal glomerulonephritis (PSGN) now primarily occurred in the developing world. This surprised me since I had diagnosed two cases that week in children in my city, very much in the middle of the US of A.

How does one cause the other?

Glomerulonephritis (GN) is a general term for inflammation of the kidney, particularly the filtering units called glomeruli. Many forms of GN can damage the kidney. Some follow infections, most commonly a strep throat or skin infection. Some forms of strep cause the body to produce antibodies that can also damage the kidney after they get trapped in the filtering membranes. These antibody levels peak 10 days – 2 weeks after a strep throat. It may take as long as 6 weeks after a strep skin infection for kidney damage to occur. The antibodies get trapped in the kidney where they cause damage and activate a system of immune proteins called complement. One particular protein in this system, C3, gets used up, so its blood levels drop.

When the kidneys suffer inflammation, they cannot filter the blood correctly. They may also leak blood and protein in to the urine. The damage may cause dark urine, swelling, high blood pressure, or even kidney failure. Some patients get kidney damage from strep, but it is so mild they never know.

Other infections can cause GN, although less commonly than strep. These include other bacteria and viruses.

Any child who presents with signs of GN should be considered for the diagnosis of PSGN and other post-infectious GN. Strep infections are common in childhood, and many families are not aware that one has occurred. Blood tests may include studies to look for evidence of a strep infection, as well as levels of C3 complement. Blood tests may be performed to rule out other causes of GN and to measure kidney function.

Kidney biopsy, obtaining and examining a piece of kidney in the laboratory, is rarely necessary in children with suspected post-infectious GN. If they fail to recover as expected, it may be needed.

There is no treatment for post-infectious GN. Medicines may be needed to treat high blood pressure and control swelling. In the most severe cases, dialysis could be necessary to replace kidney function.

By the time GN develops, the infection causing it may be gone. Antibiotics may not always be needed.

More than 90% of children with post-strep GN recover completely within a few months. In general, the milder the initial problems, the faster the recovery. Most children will have normal C3 levels in 6 weeks. If the C3 remains low for longer than 6 months or its levels go up and down, then other types of GN should be considered. Adults do not do as well as children, in part because they may have preexisting kidney damage. This seems to be especially true for adults with diabetes and its kidney damage.
Small amounts of blood, detectable only by dipstick or examination with a microscope, may remain in the urine for 2 years after an episode of GN. This microscopic hematuria is not concerning.

You can download a PDF of this information here.

Images obtained from Wikimedia Commons (strep throat and hematuria) and used under the terms of the GNU Free Documentation License.

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