Post-Infectious Glomerulonephritis

What is post-infectious glomerulonephritis?

Each kidney has about a million tiny filters called glomeruli. In PIGN, parts of bacteria (antigens) and the antibodies the body makes against them form immune complexes that lodge in the glomeruli. These activate the complement system, part of the immune defense, and white cells rush in. The inflamed filters leak blood and protein into the urine and filter less well, so salt and water are retained.

This produces the nephritic syndrome: blood in the urine, swelling, high blood pressure and reduced kidney function. See nephritic syndrome.

Post-streptococcal vs other post-infectious forms

The classic childhood form has its own page: post-streptococcal glomerulonephritis. Because adult cases often occur during an active infection, many kidney specialists now prefer the term infection-related glomerulonephritis.

Causes

• Group A streptococcus: strep throat and impetigo with certain "nephritogenic" strains. Still common in children in low-income settings and in some Indigenous communities.
• Staphylococcus aureus, including MRSA: diabetic foot ulcers, cellulitis, bone and joint infections, pneumonia.
• Infective endocarditis: infection of a heart valve, a cause in IV drug users and people with prosthetic valves.
• Infected shunts (shunt nephritis), for example a brain shunt.
• Other bacteria: gram-negative organisms, pneumococcus.
• Viruses and parasites: hepatitis B and C, HIV and malaria can cause related immune-complex kidney diseases.

Risk factors in adults

Diabetes, older age, alcohol misuse, cancer, IV drug use and other conditions that weaken immunity increase both the risk and the severity.

Symptoms

Some people have no symptoms and the disease is found only on urine tests. When symptoms appear, they include:

• Dark urine: cola, tea or smoky colored, from red blood cells (hematuria)
• Swelling (edema): puffy eyelids, worse in the morning, and swollen ankles and legs
• High blood pressure: headaches, sometimes confusion or seizures in severe cases
• Less urine than usual
• Breathlessness from fluid on the lungs
• tiredness, nausea or loss of appetite
• foamy urine if protein loss is heavy

In adults, symptoms of the underlying infection, such as fever, a leg ulcer or a heart murmur, may still be present.

How it is diagnosed

1. Urinalysis: blood and protein, with red cell casts under the microscope, a hallmark of glomerular inflammation.
2. Blood tests: creatinine and urea for kidney function, electrolytes, and urine protein-to-creatinine ratio.
3. Complement levels: low C3 is typical and usually returns to normal within 8 to 12 weeks. If C3 stays low beyond that, another disease such as C3 glomerulopathy or lupus is considered.
4. Evidence of infection: throat or skin swab, ASO and anti-DNase B antibody tests for strep, blood cultures and imaging for staph infection, and a heart ultrasound if endocarditis is possible.
5. Kidney biopsy: not needed in typical childhood cases. It is often done in adults, when kidney function falls fast, or when the course is unusual.

Treatment

There is no specific medicine to switch off the kidney inflammation. Treatment is supportive:

• Treat the infection: antibiotics for an active strep or staph infection. Treating strep early may not prevent nephritis but stops spread to others.
• Control fluid and salt: salt restriction, fluid limits and diuretics (water pills) for swelling and breathlessness.
• Lower blood pressure: diuretics first, with other medicines if needed.
• Monitor kidney function: most people need regular blood and urine tests.
• Dialysis: short term if kidney failure is severe, fluid overload cannot be controlled, or potassium becomes dangerously high.
• Steroids and immunosuppression: generally not used, and they can worsen an active infection. They are considered only in rare severe cases with crescents on biopsy once infection is controlled.

Outlook

• Children: most recover fully. Swelling and blood pressure improve within 1 to 2 weeks, visible blood clears within a few weeks, but microscopic blood can persist for up to a year and protein for longer. Recurrence is rare.
• Adults: recovery is less predictable. Many have persistent kidney impairment, and some progress to chronic kidney disease or need long-term dialysis, especially older adults with diabetes.

Long-term follow-up of blood pressure, urine protein and kidney function is recommended.

Frequently asked questions

What causes post-infectious glomerulonephritis?

It is caused by the immune system's response to an infection, not by the infection reaching the kidney. Immune complexes deposit in the kidney filters and cause inflammation. Common triggers are strep throat and impetigo in children and staph infections in adults.

What are the first signs of post-infectious glomerulonephritis?

The first signs are usually cola or tea-colored urine and puffy eyelids, often in the morning, followed by swollen ankles, less urine and high blood pressure. In children these appear 1 to 3 weeks after strep throat or 3 to 6 weeks after a skin infection.

Is post-infectious glomerulonephritis contagious?

The kidney inflammation itself is not contagious. The strep or staph infection that triggered it can spread to others, which is why outbreaks of post-streptococcal disease sometimes occur in families and communities.

How long does it take to recover?

In children, swelling and high blood pressure settle within about 2 weeks, and kidney function usually returns to normal within weeks. Microscopic blood in the urine may persist for months. Adults, especially those with diabetes, may take longer or not recover fully.

How is it different from other types of glomerulonephritis?

PIGN follows an infection, has low complement C3 that recovers within about 8 to 12 weeks, and usually improves by itself. Other types, such as IgA nephropathy or lupus nephritis, have different triggers, patterns on biopsy and often need immunosuppressive treatment.