IgA nephropathy (sometimes misspelled as “IgA neuropathy”) is a kidney disease in which an abnormal form of the antibody IgA builds up in the kidneys, causing inflammation and gradual damage to the organ’s filtering units. It’s the most common form of glomerulonephritis worldwide, and it can range from a slow, barely noticeable condition to one that leads to kidney failure over 10 to 20 years. The disease is also called Berger disease, after the physician who first described it.
How IgA Nephropathy Damages the Kidneys
Your immune system normally produces IgA antibodies to protect mucous membranes in the throat, gut, and airways. In IgA nephropathy, the body produces a defective version of one subtype, IgA1, that is missing a sugar molecule (galactose) from its structure. This defect sets off a chain reaction researchers describe as a “four-hit” process.
First, levels of this galactose-deficient IgA1 rise in the bloodstream. On its own, that isn’t enough to cause kidney damage. In the second step, the immune system recognizes the abnormal IgA1 as foreign and produces antibodies against it. Those antibodies bind to the defective IgA1, forming clumps called immune complexes (the third hit). These complexes travel through the blood and lodge in the mesangium, a tissue layer inside the kidney’s tiny filters (glomeruli).
Once trapped there, the immune complexes trigger the fourth hit: mesangial cells begin to multiply and release inflammatory signals, including compounds that promote scarring. Over time, this damages the glomerular basement membrane, the thin barrier that normally keeps blood cells and large proteins inside your blood vessels. When that barrier breaks down, blood and protein leak into the urine.
Common Symptoms and How They Appear
The hallmark sign of IgA nephropathy is blood in the urine. For some people, this is visible (macroscopic hematuria), turning urine pink, red, or cola-colored. This dramatic episode often happens at the same time as a cold, sore throat, or other upper respiratory infection, a pattern called synpharyngitic hematuria. Unlike post-streptococcal kidney disease, where blood appears in the urine one to two weeks after an infection, IgA nephropathy causes hematuria right alongside the illness.
That said, only about 10% to 15% of adults with IgA nephropathy actually experience visible bloody urine, and it’s most common in people under 40. The majority have microscopic hematuria, meaning blood is only detected on a urine test. Many also have protein in their urine (proteinuria), which often causes no symptoms at all until kidney function has declined significantly. Some people are diagnosed only after routine blood or urine tests reveal abnormalities.
As the disease progresses, symptoms of declining kidney function can develop: swelling in the hands and feet, high blood pressure, fatigue, and foamy urine from excess protein loss.
What Triggers the Disease
IgA nephropathy has a genetic component. Certain people are predisposed to produce higher levels of the defective IgA1, and the disease clusters in some families and ethnic groups (it is more common in people of Asian and European descent).
The triggers that push the disease into activity appear to come from the mucous membranes. Upper respiratory infections are the most recognized trigger. Tonsils play a significant role: patients with IgA nephropathy have unusually high numbers of IgA-producing immune cells in their tonsils, even higher than people with recurrent tonsillitis. When microbes stimulate these cells, they can ramp up production of the defective IgA1 and release it into the bloodstream.
Gut infections and chronic exposure to intestinal bacteria have also been implicated. Researchers have found that bacterial components can alter the way immune cells process the IgA1 molecule, promoting the galactose deficiency that starts the four-hit cascade. These IgA-producing cells can migrate to the bone marrow and continue releasing the abnormal antibody long after the original infection resolves, which is one reason the disease persists.
How IgA Nephropathy Is Diagnosed
A kidney biopsy is the only way to confirm IgA nephropathy. Blood and urine tests may raise suspicion, particularly when they show microscopic hematuria combined with proteinuria, but the definitive finding is the presence of dominant or codominant IgA deposits in the mesangium under a microscope. Pathologists look for these deposits using immunofluorescence staining on the biopsy tissue and typically confirm them with electron microscopy, which reveals dense deposits in the mesangial region.
Once the diagnosis is confirmed, the biopsy is graded using the Oxford classification system, sometimes called the MEST-C score. This scoring system evaluates five features of the tissue: mesangial hypercellularity, endocapillary hypercellularity, segmental scarring, tubular atrophy with interstitial fibrosis, and the presence of crescents (a sign of severe inflammation). Each of these features independently predicts how the disease is likely to progress, so the MEST-C score helps guide treatment decisions.
Long-Term Outlook and Progression Risk
IgA nephropathy is not a short-term illness. It tends to progress slowly, and many people live with it for years before experiencing serious kidney problems. But the long-term numbers are sobering. A large study published in the Clinical Journal of the American Society of Nephrology found that the median kidney survival (time before kidney failure or death) was 11.4 years, with a mean age at kidney failure of 48. At 10 years, about 54% of patients had not yet reached kidney failure. By 20 years, that number dropped to roughly 29%.
Protein in the urine is one of the strongest predictors of progression. Even patients with relatively modest proteinuria face meaningful risk: approximately 20% of those with the lowest levels of sustained protein loss developed kidney failure within 10 years. Among those with moderately elevated proteinuria, the 10-year rate climbed to around 30%. This is why reducing proteinuria is a central goal of treatment.
Treatment Options
For many years, treatment focused mainly on controlling blood pressure and reducing protein in the urine. Medications that block the renin-angiotensin system (commonly prescribed blood pressure drugs) remain the foundation of care because they lower pressure inside the kidney filters and reduce protein leakage.
More targeted therapies have recently become available. The FDA has approved a targeted-release formulation of the steroid budesonide (sold as Tarpeyo) specifically for IgA nephropathy. Unlike standard oral steroids, this version is designed to release the drug in the part of the intestine where much of the abnormal IgA production originates, aiming to reduce the immune response at its source while limiting the side effects of whole-body steroid exposure.
Another approved option, sparsentan (Filspari), works by blocking two pathways simultaneously: endothelin and angiotensin II receptors. It was initially approved to slow kidney function decline in adults with IgA nephropathy at risk for progression. Because of potential liver-related side effects, it’s available only through a restricted distribution program. For people who progress to kidney failure despite treatment, dialysis or kidney transplantation becomes necessary, though IgA nephropathy can recur in a transplanted kidney.
Monitoring After Diagnosis
Once diagnosed, regular monitoring of kidney function is essential. The two key measurements are the estimated glomerular filtration rate (eGFR), which tracks how well the kidneys filter waste, and the urine protein-to-creatinine ratio, which measures how much protein is leaking. Trends in these numbers over months and years matter more than any single result. A steadily rising protein level or a falling eGFR signals that the disease is progressing and may prompt a change in treatment strategy.
Blood pressure monitoring is equally important, since high blood pressure both results from and accelerates kidney damage. Most people with IgA nephropathy will need lifelong follow-up, even during periods when the disease appears stable, because progression can happen gradually without obvious symptoms.