IgA Nephropathy vs. IgA Vasculitis: What's Different?

The main difference between primary IgA nephropathy (IgAN) and IgA vasculitis (IgAV) with kidney involvement is where the disease is active in your body. It is completely understandable to feel confused when two different conditions share similar kidney biopsy results.

Primary IgA nephropathy is a condition that is generally limited to the kidneys ^[1]. IgA vasculitis (formerly known as Henoch-Schönlein purpura) is a systemic condition—meaning it affects multiple systems in the body, typically involving the skin, joints, and gastrointestinal (GI) tract, in addition to the kidneys ^[2]. Because the kidney damage in both conditions overlaps substantially under a microscope, doctors rely on your full-body symptoms, medical history, and physical examination to tell them apart ^[3].

Why the Kidney Biopsy Isn’t Enough

If you undergo a kidney biopsy, the results for IgA nephropathy and IgA vasculitis will look very similar ^[3]. In both conditions, the biopsy shows deposits of an antibody called Immunoglobulin A (IgA) in the glomeruli (the filtering units of the kidneys) ^[1].

While researchers have noted some general trends—such as IgA nephropathy biopsies showing more chronic scarring, and IgA vasculitis biopsies showing more active inflammation or crescents (areas of active cellular inflammation in the filtering units, which can later lead to scarring)—these are only group tendencies, not strict rules ^[4]. A doctor cannot reliably diagnose one condition over the other based on a kidney biopsy alone ^[5]. Diagnosing primary IgA nephropathy requires doctors to first evaluate your medical history and run tests to rule out IgA vasculitis and other secondary causes ^[1].

The Key Differences in Symptoms

Because the kidneys look the same in both diseases, your doctor will look for extra-renal (non-kidney) symptoms that are the hallmarks of IgA vasculitis. These include:

• Palpable purpura: This is a distinctive, raised, purple-red skin rash that doesn’t turn white when you press on it ^[2]. It is most commonly found on the lower legs and buttocks ^[1].
• Joint pain or swelling: Arthralgia (joint pain) or arthritis (joint inflammation) is very common in IgA vasculitis ^[2].
• Abdominal pain and GI bleeding: Severe, crampy abdominal pain, vomiting, or blood in the stool are critical signs of IgA vasculitis ^[6].

Urgent Symptoms Warning: If you experience severe or worsening abdominal pain, persistent vomiting, bloody or black stools, fainting, or marked abdominal swelling, seek immediate medical attention. While serious complications are uncommon, they require urgent assessment ^[2].

Timing can be tricky. While the purpura (rash) often leads to an earlier diagnosis of IgA vasculitis, kidney symptoms can sometimes appear before the rash ^[4]. In rare cases, the telltale rash may not appear until much later, but usually, it happens before or around the same time as other symptoms ^[5].

At a Glance: Comparing the Conditions

Testing and Comprehensive Evaluation

When you have kidney findings like blood in the urine (hematuria) or protein in the urine (proteinuria), a full-body history and examination are vital ^[1]. No single blood test separates primary IgAN from IgAV, so your medical team will likely:

• Perform a full physical exam: Doctors will specifically check your skin, joints, and abdomen for signs of systemic vasculitis ^[2].
• Monitor blood and urine: Checking your blood pressure, estimated glomerular filtration rate (eGFR - a measure of kidney function), and the amount of protein in your urine helps doctors assess the severity of kidney involvement ^[7].
• Help evaluate for secondary causes: Blood work can help evaluate if your symptoms might be related to other issues that cause IgA deposits, such as chronic liver disease, infections, or other autoimmune conditions ^[8].

How Management and Follow-Up Differ

Your long-term care will look different depending on your diagnosis. Note: Never change medication doses on your own, and do not start taking NSAIDs (like ibuprofen or naproxen) without asking your doctor, as these can worsen kidney function or GI bleeding.

Managing IgA Nephropathy:
Treatment focuses on long-term kidney protection. The main goals are lowering the amount of protein in your urine and keeping your blood pressure at an individualized target set by your doctor (often aiming for a top number below 120 mm Hg, if tolerated) ^[9]. This is usually done with lifestyle changes (like reducing dietary salt) and medications that protect the kidneys, such as ACE inhibitors or ARBs, and sometimes SGLT2 inhibitors if you meet specific clinical criteria ^[10]. Stronger medications that suppress the immune system are not for everyone; they are generally reserved for patients who remain at high risk of kidney decline despite initial supportive treatments ^[1].

Managing IgA Vasculitis:
Care for IgA vasculitis addresses both the systemic illness and the kidneys. Severe joint or gastrointestinal pain may require specific supportive care, specialist assessment, and sometimes carefully selected corticosteroid therapy ^[2]. Crucially, the kidney problems in IgA vasculitis can appear without noticeable symptoms many weeks after the initial skin rash or stomach pain has gone away ^[6]. For this reason, serial monitoring of your urine and blood pressure is highly recommended for at least six months after an IgA vasculitis flare ^[11]. If you do develop established kidney disease from IgA vasculitis, you will need ongoing, long-term nephrology follow-up, similar to primary IgA nephropathy.