What Is Complement 3 Glomerulopathy?

Written by Sarah Amandolare
Medically Reviewed by Neha Pathak, MD on November 14, 2025

Also called C3G, this rare kidney disease often affects children and young adults, but it can happen at any age. It has a major impact on a person’s health and life. 

C3G has two forms: dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). Either form can be caused by genetic issues that may or may not be inherited, or by health complications that happen during life. In both, there are problems with the complement system, which helps fight infections in your body. 

Small filters in your kidneys called glomeruli clean your blood and help keep you healthy. In DDD and C3GN, damaged glomeruli allow proteins, along with red and white blood cells, to get into your urine. This messes with your kidney function. Over time, this damage can lead to kidney failure. 

Some studies show DDD may affect younger people more than C3GN does.

 

Each person with C3G may have different symptoms, so it’s important to know all possible signs. 

 

 

Your doctor will use a kidney biopsy to see if you have C3G. It’s the only way to get a correct diagnosis. In this procedure, they’ll remove a small piece of your kidney to examine in a lab. You may also have genetic testing or blood and urine tests.

Once you get a diagnosis, you may want to ask your doctor some questions to learn more about your condition.

 

 

With C3G, your team will likely include your primary doctor plus a nephrologist (a doctor who specializes in kidney problems), a hematologist (a doctor who works with blood diseases), a transfusion medicine team (who’ll test your blood), a pathologist (a doctor who examines tissue samples), and a laboratory medicine team.

 

When you're still coming to terms with having C3G, the thought of finding a team of doctors may seem overwhelming. Asking for support from organizations and people you trust can help you manage this process. 

  • Start with your primary care doctor, who may refer you to a nephrologist. 
  • Consult patient advocacy groups and organizations, such as NephCure, which has an online directory of rare kidney disease specialists. 
  • Focus your search on Centers of Excellence, which are hospitals or medical institutions with highly trained teams of doctors and researchers focused on specific diseases. Centers of Excellence often work to discover new treatments and cures, which can give you access to cutting-edge medicines and clinical trials. 
  • Check the National Organization for Rare Disorders (NORD), which has an online directory of Centers of Excellence searchable by location. NORD also lists ongoing clinical trials of treatments for rare diseases, including C3G. 
  • Go out-of-network. You may decide to seek care from a C3G specialist in another state or outside your insurance network. This can require getting an out-of-network exception from your insurance company. Organizations can help you navigate this process. 
    • The Patient Advocate Foundation can assign a case manager to work on your behalf to challenge insurance denials and gain prior authorization. 
    • NORD provides financial assistance for patients struggling to pay for insurance premiums, diagnostic tests, and travel for clinical trials or consultations with rare disease specialists. 
    • The National Kidney Foundation provides online resources to help you find affordable health care and prescription drug assistance. 

Ask questions before you decide where to be treated for C3G, says Kirk Campbell, MD, president of the National Kidney Foundation and director of the Mount Sinai Center for Kidney Disease Innovation. For example, ask if a hospital offers advanced complement testing studies. You can also ask if a center hosts any clinical trials of complement inhibitors. 

"It's important to have a frank discussion with the physician managing C3G," says Campbell. For example, you can ask how many C3G patients they take care of. And don’t hesitate to ask for a second opinion. “It's not inappropriate to request a referral to a specialist, and it doesn't mean that the relationship with the primary nephrologist is going to end,” Campbell says. “Patients are very often co-managed with more than one nephrologist being involved in the care, and then they communicate and help each other.” 

There’s no single best treatment for C3G, and research into new therapies is ongoing. But there are some that might help you feel better. 

For example, treatments that focus on your blood pressure control and proteinuria may slow down the progression of C3G. That’s because they may help reduce the amount of protein spilling into your urine. They include:

  • Angiotensin-converting enzyme (ACE) inhibitors, such as benazepril (Lotensin), enalapril (Epaned, Vasotec), lisinopril (Qbrelis, Zestril), and ramipril (Altace)
  • Angiotensin II type-1 receptor blockers (ARBs), such as losartan (Cozaar), olmesartan (Benicar), and valsartan (Diovan)
  • Endothelin and angiotensin II receptor antagonists, such as sparsentan (Filspari)

And if you have high cholesterol, drugs prescribed to lower your cholesterol may also help reduce problems in other parts of your body. Research shows they may slow down the rate of your C3G getting worse. 

Another option may be a combo of glucocorticoids and mycophenolate mofetil (MMF). These are drugs that suppress your immune system. Studies show they may help prevent relapses of C3G in some people. 

Also, an anti-complement drug called eculizumab (Soliris) might help lower your proteinuria and slow down your progression of C3G. 

New therapies being studied for treatment of C3G include the drug iptacopan (LNP023). The FDA gave this drug a breakthrough therapy designation and a rare pediatric disease designation. That means research into its effectiveness for C3G will be fast-tracked. 

Pegcetacoplan (Empaveli) is an FDA-approved complement inhibitor to treat C3G in people 12 and older. This medicine helps to “turn down” your hyperactive immune complement system. That helps to reduce the C3 protein that goes through your kidneys and into your urine.

The main complication of C3G is the progression of kidney disease from chronic to end-stage disease. "About half of patients will progress to kidney failure in about 10 years, based on publicly available data," Campbell says. 

The two treatment options for kidney failure are dialysis (to remove excess fluid and wastes from your blood) or kidney transplant. 

Dialysis can affect your quality of life. You may receive treatment daily, need to restrict your diet, and have difficulty getting around and traveling.  

A kidney transplant is "a much better option compared to dialysis," Campbell says, but there's a high risk of C3G coming back. Recurrence rates of C3G after a kidney transplant are "widely variable," ranging from 40% to 80% or higher, Campbell says. "It's important for the transplant nephrologist and the general nephrologist managing patients post-transplant to monitor closely for any sign of recurrence. That typically involves close monitoring of kidney function [for] evidence of blood or protein in the urine,” Campbell says. 

Having C3G also puts you at greater risk for complications associated with chronic kidney disease and end-stage kidney disease, such as high blood pressure, anemia, mineral and bone disease, metabolic acidosis, and cardiovascular disease. 

Certain C3G medications, especially complement inhibitors, carry a risk of infections, such as meningitis.

In addition to your medical treatment, it’s important that you look after yourself if you have C3G. To do so, make sure you:

Eat a healthy diet. Fill your meals with fruits, vegetables, starchy and whole-grain foods, and foods with low saturated fats, salts, and sugars. Keep some dairy and other sources of protein (like fish, beans, or meat) in your diet as well.

Your doctor may have you limit your potassium, sodium, or phosphate.

A well-balanced diet can help you avoid other issues alongside your C3G.

Stay on top of your health. Even if you feel great, it’s important that you stick to your routine and take all your meds. Always tell your doctor if you have any concerns or strange symptoms. If you take other drugs or supplements, tell your doctor to make sure they don’t interact with your C3G treatment.

Exercise. Proper physical activity will help you sleep, boost your energy, keep your bones strong, and help you ward off depression. Exercise also lowers your risk of heart disease and other complications.

If you’re on dialysis, you may not be able to exercise as much. Ask your doctor about the best exercise plan for you. 

Stop smoking. This will improve your overall health. Ask your doctor if you need help quitting.

Limit alcohol. Ask your doctor if it’s OK to drink in moderation. Let them know If you need help cutting back or stopping.

After your C3G diagnosis, your care team will help you find the best treatment plan. You might be able to join a clinical trial. But those might be hard to find since this is a rare disease.

In severe cases, you might eventually have dialysis or a kidney transplant. But there’s a high chance of C3G coming back after a transplant. Talk to your doctor about the best options for you.

Over the long term, C3G can take a toll on your day-to-day well-being. It's common to experience chronic physical discomfort or pain. Many people with C3G also feel tired and weak and need to nap during the day. You might have difficulty staying active, preparing meals, or washing and dressing yourself, so you may need help from a home health aid, family, or friends. 

Your symptoms may get worse. About half of people with C3G eventually get end-stage renal disease, or ESRD. This often happens within 10 years of your diagnosis.

ESRD, which is life-threatening, means your kidneys can’t filter fluids and waste from your body well enough.

To find support, look into the National Organization for Rare Disorders (NORD) or Disease Info Search. There’s also an online support community for those living with C3G. It’s provided through the National Kidney Foundation. 

To learn more about your possible risk for C3G, ask your doctor about genetic testing.

Fatigue, swelling, and fluid retention from C3G can prevent you from doing your usual activities. You may feel isolated and frustrated because you can't do the things you love or socialize as much as you used to. You may also have difficulty sleeping, a low appetite, less energy than usual, and feel more irritable, anxious, and depressed. 

"This is expected and not to be ashamed of,” Campbell says. "Inflammatory conditions, like this chronic kidney disease in particular, can be associated with emotional and mental burdens.” 

Taking proactive steps can help you cope with the emotional challenges of C3G: 

  • Patient advocacy groups can direct you to counseling services specifically for people with this disease. 
  • Connecting with others facing similar emotional and physical challenges can help you feel less alone and may make day-to-day life a little easier. 
  • The National Kidney Foundation's Peer program can connect you with support groups for C3G patients or groups for people getting dialysis. You can also sign up to be a peer mentor for others. 

If you’re feeling stuck, reach out to your care team for help finding the resources you need. “Having that honest conversation with providers to get the appropriate support is crucially important,” Campbell says. 

Being a caregiver for someone with a rare disease like C3G is often highly stressful. You may feel isolated because the condition isn't common or well understood within your community, leading you to withdraw from friends and family. Thinking about the disease progressing in the future could make you feel anxious. There are also numerous responsibilities for caregivers, such as managing insurance claims and making frequent visits to doctors and hospitals. Over time, caregiving can take a serious toll on your mental health. 

"Burnout is definitely real, and that applies to the patients as well as the caregivers," Campbell says. 

Professional mental health support, such as therapists and counselors, can help you navigate burnout. Many supportive online communities are also available for caregivers.

  • The National Kidney Foundation provides links to many other organizations focused on supporting caregivers and families of people with rare kidney diseases. 
  • Nephcure offers guided support groups for parents of children with kidney diseases. 
  • The Rare Genomics Institute links to online platforms where caregivers can find others in similar situations. 

"Folks can compare notes and learn barriers and facilitators to good emotional and physical health," Campbell says. 

As the caregiver, it's also important to take care of your own physical health. Campbell says to:

  • Get enough sleep 
  • Keep up with your own medical and dental care
  • Eat healthy foods
  • Exercise

Even light movement, like yoga or walking, can be beneficial to your mental and physical health. Mindfulness and meditation, as well as journaling, can help you manage and process your emotions. 

Organizations for rare diseases, including the National Kidney Foundation, provide online wellness guides that cover nutrition and exercise tips for people with kidney disease. These guides can also help caregivers looking for advice to use in their own lives. 

If you're feeling overwhelmed, it's important to share the load, Cambell says. That could mean asking for another family member or caregiver to help with day-to-day challenges, such as transportation to medical visits, pharmacy runs, and dealing with insurance issues. 

C3G is a rare kidney disease that often affects children and young adults, but it can be diagnosed at any age. Symptoms can be different for everyone, so it's important to understand all the possible signs and symptoms, from dark urine to swelling in hands and feet. Managing C3G can feel overwhelming and isolating at times, but remember that others are facing similar challenges and there are many sources of support for patients and caregivers. Research is ongoing to find new treatments.

How is C3G diagnosed? 
A C3G diagnosis requires a kidney biopsy showing complement dominant deposits. Additional testing is often needed to understand what's causing the disease.

Is C3G genetic? 
It can be. C3G is often caused by autoantibodies that arise because of different factors, such as your environment. But the disease can also be caused by genetic variants that affect complement regulation. 

What's my risk of C3G progression or kidney transplant and recurrence after transplant? 
About half of people with C3G progress to kidney failure in about 10 years. After a kidney transplant, the risk of C3G recurrence varies widely, ranging from 40% to 80% or greater risk of recurrence. 

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