IgA nephropathy is a kidney disease where an abnormal form of a common immune protein, called IgA, builds up in the kidneys and causes damage over time. It is the most common primary kidney-filtering disease worldwide, with a global incidence of about 2.5 per 100,000 people per year. Also known as Berger’s disease, it ranges from mild cases that barely cause symptoms to aggressive forms that can lead to kidney failure. About 21% of patients reach kidney failure or death within 10 years of diagnosis, and that number rises to roughly 33% at 20 years.
How the Immune System Damages the Kidneys
IgA is an antibody your body normally produces to fight infections, especially in the lining of the gut and airways. In people with IgA nephropathy, a portion of their IgA1 molecules are made incorrectly: they’re missing a sugar molecule called galactose on a specific part of the protein chain. This defective IgA1 circulates in the blood at higher-than-normal levels.
The disease follows a four-step chain reaction. First, the body overproduces these galactose-deficient IgA1 molecules. Second, the immune system recognizes them as foreign and creates antibodies against them. Third, those antibodies bind to the defective IgA1 and form clumps called immune complexes in the bloodstream. Fourth, some of those immune complexes get trapped in the mesangium, a network of cells inside the kidney’s filtering units (glomeruli). Once lodged there, they trigger inflammation that gradually scars and destroys kidney tissue.
Who Gets IgA Nephropathy
Geography and ancestry play a significant role. The disease is most common in East Asia, where it accounts for 30 to 40% of all kidney-filtering diseases found on biopsy. In Japan, the annual incidence runs between 3.9 and 4.5 per 100,000 people; in China, it’s about 3.8. European countries report moderate rates, typically between 1.3 and 2.9 per 100,000. In the United States, the incidence is 1.3 to 2.2 per 100,000, and rates are lowest in sub-Saharan Africa, though limited access to kidney biopsies likely contributes to underreporting there.
Genetics matter, too. Large-scale genetic studies have identified at least seven regions of DNA linked to the disease, many of them clustered in genes that regulate the immune system. The tendency to produce defective IgA1 appears to be heritable in a dominant pattern, meaning it can pass through families. Having a first-degree relative with the condition increases your risk.
Common Symptoms
The hallmark sign is blood in the urine. In its most dramatic form, this appears as visibly dark or tea-colored urine, often triggered by an upper respiratory infection like a sore throat or cold. About 80% of these visible-blood episodes coincide with throat or tonsil infections, typically showing up within 48 to 72 hours of the infection starting. The bloody urine usually lasts less than three days and, in about a third of cases, comes with a dull ache in the lower back from kidney swelling.
Many people, however, have no obvious symptoms at all. Their disease is discovered incidentally when a routine urinalysis detects microscopic amounts of blood or protein. Other presentations include persistent protein in the urine (usually under 3 grams per day), high blood pressure, and, less commonly, full-blown nephrotic syndrome with heavy protein loss, swelling, and elevated cholesterol. A small number of patients present with rapidly worsening kidney function that can progress to kidney failure quickly.
How It Is Diagnosed
A kidney biopsy is the only way to definitively diagnose IgA nephropathy. No blood test or urine marker can confirm it on its own. During a biopsy, a small sample of kidney tissue is examined under a microscope, where pathologists look for IgA deposits in the mesangium of the glomeruli.
Once a biopsy confirms the diagnosis, the tissue is scored using a standardized system called the MEST-C classification. This evaluates five features of kidney damage: how much the mesangial cells have multiplied (M), whether the cells inside the capillary loops are inflamed (E), how much scarring exists in the filtering units (S), how much the surrounding tissue has wasted away or become fibrotic (T), and whether crescent-shaped lesions have formed (C). Each of these features independently predicts how the disease is likely to behave, helping doctors estimate your risk of progression and tailor treatment intensity.
Treatment Options
Because the disease varies so much from person to person, treatment is highly individualized. The foundation for nearly everyone is controlling blood pressure and reducing protein in the urine, since persistent proteinuria is one of the strongest predictors of kidney decline. Medications that block the effects of angiotensin, a hormone that raises blood pressure and stresses the kidneys, are the standard first step.
For patients with significant proteinuria (at or above 1 gram per day) who don’t respond adequately to these standard measures, newer targeted therapies are now available. Sparsentan (brand name Filspari) blocks two pathways that contribute to kidney damage simultaneously. In a major clinical trial, it reduced proteinuria by about 50% from baseline, compared with roughly 15% for a conventional angiotensin blocker alone. Another option, targeted-release budesonide (Tarpeyo), is an anti-inflammatory steroid formulated to act specifically in the gut, where much of the problematic IgA is produced. It’s typically added on when there’s a risk of rapid disease progression. These two medications work through different mechanisms and are often used together rather than as alternatives.
Diet and Lifestyle
Dietary changes won’t cure IgA nephropathy, but they can meaningfully slow progression and reduce the burden on your kidneys. Keeping sodium intake low is the single most impactful dietary change. The recommended target is no more than 1,500 milligrams per day, which means cooking from scratch more often and reading labels carefully, since processed and restaurant foods are the biggest sodium sources for most people.
Beyond sodium, the general guidance is to build meals around nutrient-dense whole foods: fruits, vegetables, fish, eggs, beans, nuts, seeds, and whole grains. Red bell peppers, berries, and fish are particularly good choices because they’re rich in vitamins and anti-inflammatory compounds while being low in potassium and phosphorus, two minerals that can accumulate when kidney function drops. If your kidney function has declined significantly or you’re on dialysis, you may need a more restrictive renal diet tailored by a dietitian. If you also have diabetes, blood sugar management becomes an additional priority.
Long-Term Outlook
IgA nephropathy is a chronic condition with a wide spectrum of outcomes. Some people have stable, mild disease for decades with little more than trace blood in the urine. Others experience a steady decline in kidney function that eventually requires dialysis or a transplant. In a large long-term study, 79% of patients had not reached kidney failure or death at 10 years, and 67% remained free of those outcomes at 20 years. That means roughly one in three patients faces serious kidney decline over two decades.
The strongest predictors of a worse outcome are persistent heavy proteinuria, high blood pressure that’s difficult to control, impaired kidney function at the time of diagnosis, and more severe findings on the MEST-C biopsy score. The disease can also recur in a transplanted kidney, though this doesn’t always lead to graft failure. Early diagnosis, aggressive blood pressure control, and the newer targeted therapies now available have shifted the outlook considerably compared with a decade ago.