A protein called FHR5 found in kidney biopsies may be a powerful predictor of which patients with ANCA-associated vasculitis will progress to end-stage kidney disease, according to new research published in Kidney International Reports. The finding could help doctors identify patients who need more aggressive treatment early on.

What Is ANCA-Associated Vasculitis and Why Does It Matter?

ANCA-associated vasculitis, or AAV, is a rare autoimmune disease that causes inflammation in small blood vessels, particularly those in the kidneys. When the kidneys are severely affected, patients can develop kidney disease that eventually requires dialysis or transplantation. Understanding which patients are at highest risk for this progression has been a major challenge for nephrologists, the doctors who specialize in kidney disease.

The new study examined 154 patients with active AAV and kidney involvement, along with 55 patients who achieved remission and 72 healthy controls. Researchers measured a protein called FHR5, which stands for complement factor H-related protein 5, in both blood samples and kidney biopsy tissue. The complement system is part of the immune system, and FHR5 appears to play a role in how the disease damages kidneys.

How Strong Is the Connection Between FHR5 and Kidney Damage?

The results were striking. Among the 71 patients who had kidney biopsies, 69% showed positive FHR5 staining in their glomeruli, the filtering units of the kidney, while normal control kidneys had no FHR5 deposits at all. More importantly, the amount of FHR5 in the kidney tissue predicted how well patients would respond to treatment.

Patients with moderate-to-strong FHR5 deposits had significantly worse outcomes. Only 19% of patients with strong FHR5 deposition achieved complete disease remission, compared with 82% of those with minimal or no deposits. Six months after starting treatment, only 20% of patients with moderate or strong FHR5 deposits showed signs of kidney recovery, while 80% experienced treatment failure. In contrast, nearly 90% of patients with negative or minimal FHR5 deposits achieved complete or partial recovery.

During follow-up, 24% of the entire study group progressed to end-stage kidney disease. While plasma FHR5 levels alone were not a reliable predictor, glomerular FHR5 deposition, meaning FHR5 found directly in the kidney tissue, strongly predicted progression to end-stage kidney disease.

How to Interpret Your Kidney Biopsy Results

• FHR5 Deposition Status: If your kidney biopsy shows negative or minimal FHR5 deposits, you have a much better prognosis, with about 90% of patients achieving kidney recovery with treatment.
• Treatment Response Prediction: Moderate-to-strong FHR5 deposits indicate a higher likelihood of treatment resistance and kidney failure, which may prompt your doctor to consider more aggressive or alternative therapies.
• Complement Activation: FHR5 co-localizes with complement proteins in the kidney, indicating that local immune activation is occurring, which helps explain why some patients have worse outcomes than others.

The research team noted that FHR5 functions as a competitive antagonist of factor H, another protein involved in immune regulation. This means FHR5 essentially interferes with the body's natural ability to control inflammation, making it a key player in AAV progression.

For patients with AAV and kidney involvement, these findings suggest that FHR5 testing on kidney biopsy tissue could become an important tool for risk stratification. Patients with high FHR5 deposits might benefit from earlier, more intensive treatment to prevent progression to end-stage kidney disease and the need for dialysis. The study provides a biological explanation for why some patients respond well to standard treatments while others do not, potentially opening the door to more personalized treatment approaches in the future.