How to Tell Primary IgA Nephropathy From Secondary IgA

Finding IgA deposits in your kidneys during a biopsy is a crucial piece of your diagnostic puzzle, but it does not automatically mean you have primary IgA nephropathy (IgAN). The diagnosis of primary IgAN is a “clinicopathologic” diagnosis. This means doctors combine the biopsy results—typically showing IgA-dominant deposits in the mesangium (the central supportive tissue of the kidney filters)—with your lab tests and symptoms ^[1]. Crucially, primary IgAN is diagnosed only when no other underlying systemic illness is found to be the cause ^{[1] [2]}.

To ensure you receive the right care, doctors must look for secondary IgA deposition—situations where another health condition drives the IgA buildup ^[1].

Why Do Secondary IgA Deposits Happen?

In primary IgAN, your body produces an abnormally shaped version of the IgA antibody (galactose-deficient IgA1) that clumps together and triggers kidney inflammation ^[1]. Secondary IgA deposits occur differently. When you have chronic liver disease, severe infections, or certain autoimmune conditions, your body’s immune regulation and its ability to clear circulating IgA can be altered, leading to deposits in the kidney ^{[3] [4]}. Sometimes, small amounts of IgA can even be “incidental,” meaning they are present but not actually causing your kidney damage ^[5].

How Doctors Check for Secondary Causes

Your care team will review your history and may order targeted tests to look for recognized secondary causes ^[1]. Finding IgA deposits does not mean you have one of these conditions; the workup is individualized based on your unique symptoms.

1. Chronic Liver Disease

The liver helps clear IgA complexes from your blood. If it is damaged, IgA can accumulate ^[3]. Doctors will ask about heavy alcohol use and check for signs of cirrhosis (liver scarring) and viral hepatitis (Hepatitis B and C) ^{[6] [7]}.

2. Autoimmune and Rheumatologic Diseases

IgA deposits can be part of broader autoimmune diseases. Important considerations include:

• IgA Vasculitis: This condition shares the same kidney findings as primary IgAN but causes systemic symptoms like a purple spotted rash (palpable purpura), joint pain, and abdominal pain ^[3].
• Lupus (Systemic Lupus Erythematosus): Lupus nephritis can closely mimic IgAN ^[8]. Doctors will evaluate you for joint pain or rashes and check specific blood markers, such as ANA (antinuclear antibodies) and complement levels ^[9].

3. Active Infections

A severe, ongoing bacterial infection (such as a staph infection on the skin or an infection in the heart valves) can cause an intense immune reaction known as IgA-dominant infection-related glomerulonephritis ^[10]. This is different from the temporary, visible blood in the urine (hematuria) that many primary IgAN patients experience during a standard common cold. To rule out an active infection-related cause, doctors will check for recent fevers, skin infections, or antibiotic use, and monitor your blood complement levels ^[11]. They may also screen for HIV, which is associated with several kidney conditions ^[12].

4. Gastrointestinal Conditions

Bowel diseases like inflammatory bowel disease (IBD) and celiac disease are associated with secondary IgA deposits ^{[13] [14]}.

Important Safety Note on Celiac Testing: If celiac disease is suspected, doctors may check your blood for tissue-transglutaminase (tTG) IgA. This test should generally be interpreted with a total-IgA measurement to avoid false negatives caused by IgA deficiency ^[13]. Do not start a gluten-free diet before testing, as this can make the test inaccurate. Always wait for your clinician’s guidance.

5. Medication Exposures

Rarely, certain medications, such as anti-TNF biologics used for inflammatory diseases (e.g., infliximab or adalimumab), have been associated with secondary IgA deposits ^{[15] [3]}.

Medication Safety: These associations are uncommon and do not definitively prove the drug caused the problem. Never stop an effective prescribed medication on your own. Discuss the risks and timing with your prescribing specialist and nephrologist.

What the Biopsy Can and Cannot Tell You

While the biopsy is essential, no single staining pattern perfectly identifies the cause ^[1]. Pathologists look for clues under microscopes, but they must be interpreted alongside your clinical picture:

• “Full-house” staining: This means the biopsy lights up with many different immune proteins (like IgG, IgM, and C1q). It raises high suspicion for lupus but is not absolute proof, as it can happen in other immune complex diseases ^{[9] [8]}.
• Subepithelial humps: These bump-like structures seen on electron microscopy support the possibility of an infection-related cause, but they do not single-handedly prove there is an active bacterial infection ^{[10] [11]}.

Why the Distinction Matters for Your Treatment Plan

Primary and secondary diseases require very different treatment approaches.

For primary IgAN, treatment generally begins with optimized supportive care, such as medications to control blood pressure and reduce urine protein (proteinuria) ^{[16] [17]}. Stronger immunosuppressants (like corticosteroids) are not routine for everyone; they carry risks like severe infections and metabolic issues, and are typically reserved only for selected patients at a meaningful risk of kidney failure ^{[17] [18]}.

For secondary IgA deposition, treatment focuses on the underlying cause. How immunosuppressants are used depends entirely on the condition:

• If an active infection is driving the kidney inflammation, giving immunosuppressants could weaken your immune system and be highly dangerous ^{[19] [18]}. Instead, antibiotics and source control are required ^[19].
• Conversely, if your secondary cause is an autoimmune disease like lupus or severe IgA vasculitis, specialist-directed immunosuppression is often a critical and necessary part of the treatment ^{[20] [21]}.
• For liver or gastrointestinal causes, treating the underlying illness (such as antiviral meds for hepatitis or managing IBD) is the priority ^{[22] [23]}.

While successfully treating the root cause of a secondary condition can halt ongoing kidney injury, it is not a guaranteed cure ^[24]. Established scarring, reduced kidney function, or proteinuria may persist, requiring long-term monitoring of your blood pressure and kidney function by your nephrologist ^[25].