IgA Nephropathy vs. Infection-Related GN: What Differs?

While primary IgA nephropathy (IgAN) is an immune-mediated kidney disease driven by abnormal IgA antibodies depositing in the kidneys, IgA-dominant infection-related glomerulonephritis (IgA-IRGN) is a distinct condition that mimics it but is driven by an active or recent bacterial infection ^[1][2]. Distinguishing between the two is critical because adding strong immune-suppressing drugs to treat what is actually an active infection can be ineffective and potentially dangerous ^[3][4]. Doctors rely on a combination of clinical risk factors, blood tests, and specific kidney biopsy patterns to tell them apart, though both conditions share a foundation of kidney-protective care ^[5].

Clinical Clues and Risk Factors

IgA-IRGN typically develops as an immune reaction to a bacterial infection, most commonly a Staphylococcus (Staph) infection ^[1]. The infection might be obvious, like a skin infection or pneumonia, but it can also be occult (hidden from plain sight), such as a deep spinal abscess or a heart valve infection ^[6][7]. However, it is important to know that a recent infection can also trigger a flare of primary IgAN, so having had a recent infection does not automatically mean the disease is infection-related ^[8][9].

Compared to typical IgAN, people with IgA-IRGN are more likely to be older adults, have diabetes, and experience sudden acute kidney injury (a rapid, dangerous decline in kidney function) ^[1][10].

Blood tests also provide clues, though they are not definitive:

• Low C3: C3 is a complement protein that acts as part of the immune system. It can get used up during certain infections, leading to lower levels in the blood ^[5][11].
• Low serum albumin: Albumin is a protein in the blood that can drop due to urinary protein loss, severe illness, or inflammation ^[5].

These findings can support a diagnosis of IgA-IRGN, but they neither establish nor exclude it. C3 can be normal in infection-related disease, and low albumin is a nonspecific finding seen in many kidney conditions.

Interpreting the Kidney Biopsy

Under a microscope, both conditions show deposits of IgA antibodies in the kidneys, which is why they are easily confused ^[2]. However, pathologists (doctors who specialize in interpreting biopsies) look for specific microscopic patterns that favor an infection-related cause:

• Endocapillary proliferation: A swelling and increase of cells inside the tiny blood vessels (capillaries) of the kidney filters, which is frequently seen in IgA-IRGN ^[5][10].
• C3 Co-dominance: While IgA is present, the biopsy staining may show equally strong deposits of the C3 complement protein ^[1].
• Subepithelial humps: When examined under a high-powered electron microscope, IgA-IRGN can produce distinct “hump-shaped” immune deposits on the outside of the capillary walls ^[12].
• Crescents: Severe, active inflammation can cause cellular crescents (collections of proliferating cells and inflammatory material) in the kidney filters ^[12][1]. These represent active, severe injury rather than just scarring.

Because none of these biopsy features are 100% exclusive to infection—for example, subepithelial humps and crescents can occasionally be seen in primary IgAN—doctors cannot rely on the biopsy alone ^[13][2]. The pathology must always be interpreted alongside the patient’s symptoms, medical history, and clinical picture.

How Treatment Differences Impact Care

Both conditions require supportive, kidney-protective care. This usually involves blood pressure medications (like ACE inhibitors or ARBs) and sometimes other protective drugs like SGLT2 inhibitors ^[9].

The primary difference lies in how the underlying inflammation is managed:

• For primary IgAN: If supportive care isn’t enough, doctors may selectively use immunosuppressants (like steroids) to quiet the overactive immune system ^[9].
• For IgA-IRGN: The absolute priority is finding and controlling the underlying infection using targeted antibiotics and, if necessary, surgical drainage of abscesses ^[14][11].

Adding strong immunosuppressants for an active, underlying bacterial infection can precipitate severe sepsis and may be fatal ^[3][4]. Only in rare, carefully selected situations—and under expert specialist guidance—might a doctor consider cautious immunosuppression if the kidneys continue to aggressively decline after the infection is completely controlled ^[15]. Never start, stop, or change immunosuppressive medications without direct instructions from your care team.

When to Seek Urgent Care

Diagnostic uncertainty can be stressful, but it is necessary to ensure safe treatment. If you experience any of the following symptoms, you should seek urgent medical assessment, as they could indicate a severe infection or rapidly declining kidney function:

• Fever, chills, or sudden confusion
• A marked reduction in how much you urinate
• Rapidly worsening swelling in your legs or face
• Shortness of breath or severe unexplained illness

At-A-Glance Comparison

Note: Overlap is common, and your care team will integrate all evidence to determine the best path forward.