How Prevalent Is IgA Nephropathy, the Most Common Cause of Kidney Inflammation

IgA nephropathy (IgAN), also known as Berger’s disease, is considered a rare disease. However, it is the main cause of kidney inflammation (glomerulonephritis) global. Cases of IgAN appear to be increasing, but experts say this reflects better detection and reporting, rather than an increase in risk.

About 60 out of 100,000 people worldwide have IgA nephropathy. In the United States, approximately 150,000 to 200,000 people carry IgAN.

Globally, there are on average two or three new cases per 100,000 people each year. Rates are the highest in East Asia. Here are the estimated annual rates of new cases per 100,000 people in several countries and continents:

• Africa: 0.5
• South America: 0.5
• Europe: 1-3
• UNITED STATES: 2
• Japan: 4.5

Reported rates of IgA nephropathy vary widely by region, but these differences do not always reflect disease risk. Genetics and ethnicity are part of the equation, but how countries screen, diagnose and track cases heavily determines the numbers.

Screening practices

IgA nephropathy appears to be more common in East Asian and Pacific countries, suggesting a higher underlying disease burden in these regions. However, screening practices also influence reported rates.

In countries like Japan, routine urine tests begin in childhood. This allows healthcare providers to detect kidney changes early and diagnose IgA nephropathy in people with mild or no symptoms. In many other areas, providers don’t routinely test healthy people, so cases often go unnoticed until a person shows symptoms.

Invasive tests needed to confirm diagnosis

A kidney biopsy is the only way to confirm IgAN. A kidney biopsy occurs when providers use a needle to remove a piece of kidney tissue to examine it under a microscope. Because biopsies are invasive and not always available, many people never receive a formal diagnosis. Milder cases often go unnoticed, while more serious cases are more likely to appear in official statistics.

How researchers measure rates

Some researchers track incidence, which is the number of new diagnoses each year. Others measure prevalence or the number of people living with the disease. Estimating these numbers is difficult because many people have no symptoms, diagnosis requires a kidney biopsy, and screening and access to care varies.

Many gather data from kidney biopsy registries, national databases or insurance claims. These sources reflect who is tested and diagnosed, but do not reflect everyone with the disease. As a result, lower rates reported in regions like South Africa may reflect underdiagnosis rather than lower risk.

Gaps in research and health care

Most studies focus on Asia, Europe and North America. There is very little data on Africa or on Black, Hispanic, and Latino populations. These gaps limit what researchers can conclude and highlight the need for larger, more diverse studies with equal access to kidney testing.

Anyone can develop IgA nephropathy, but the likelihood varies depending on:

• Ethnic origin: IgAN is more common in people of Asian ancestry.
• Gender: Men are at two to three times higher risk in North America and Europe, but the risk is similar between sexes in Asian populations.
• Age: IgAN is more common in people aged 10 to 40 years.
• Genetic: IgAN is not transmitted like eye color. However, if you have genetic variations in the HLA region (and in certain other genes), you are at higher risk of developing IgAN. Having these genes does not mean you will develop the disease, as it represents less than 10% of your risk.
• Family history: Most cases of IgAN occur randomly, without a family history. Fewer than 1 in 10 people with IgAN have a close relative who is a carrier. However, sometimes abnormal IgA (the antibody that clumps together and causes problems) is hereditary. About 1 in 4 close relatives may have higher levels of this abnormal IgA in their blood, but most of them will never develop kidney disease.
• Lifestyle factors: Certain lifestyle choices can be particularly hard on your kidneys, increasing your risk. For example, high blood pressure and smoking damage the blood vessels in your kidneys, and carrying excess weight makes your kidneys work harder.
• Infections and health problems: Symptoms of IgA nephropathy often flare up after infections, especially a cold, sore throat, or respiratory infection. These infections do not cause disease, but they can trigger immune responses that cause or worsen symptoms. IgA nephropathy also occurs more often alongside certain health conditions, including autoimmune diseases and liver disease.

Contact a healthcare professional if you notice symptoms of IgAN, such as:

• Dark, pink, red, or cola-colored urine
• Foamy urine
• Swelling of the face, hands, feet, or ankles
• Fatigue or headache that does not improve
• Abdominal pain

Your provider may use risk assessment tools that combine lab results, blood pressure, and medical history. If you are at high risk, they may periodically check your urine for protein and monitor your kidney function with blood tests.