Complement 3 glomerulopathy (C3G) is a set of rare kidney diseases caused by overactivation of a part of the immune system called the complement system. Glomerulopathy refers to the damage done to the tiny filtering units in the kidneys known as glomeruli. Your kidneys are responsible for filtering out waste and fluid — when these organs become damaged, you may start to notice changes in your urine or swelling due to fluid buildup.

Knowing the symptoms of C3G can help you identify the disease sooner rather than later. Your doctor or nephrologist (kidney specialist) will develop a tailored treatment plan to help control your symptoms and reduce the chances of C3G progressing to renal (kidney) failure.

What Is C3 Glomerulopathy?

C3G is made of two forms of kidney disease — C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). These conditions are caused by abnormal activation of the complement system, an important part of your immune system that helps protect your body against bacteria and viruses.

The complement system is made of nearly 50 proteins, including C3. During infections, this important protein is broken down to help produce inflammation and trigger other complement proteins to kill bacteria and viruses. However, activation of the complement system outside of infections can be damaging. Some people have mutations in genes that help regulate this system, like brakes in a car. When these genes don’t work properly, inflammation can become uncontrollable.

The kidneys are especially sensitive to this inflammation — broken-down C3 proteins can get stuck in the glomeruli, damaging them and causing scarring. This affects your kidney function, preventing the proper filtration of your blood to remove waste and fluid. Your doctor may order a blood test to measure your glomerular filtration rate, or how much blood is filtered through your kidneys every minute.

Toxins and extra fluid also begin building up, which can damage your kidneys even more. If it’s not treated in time, C3G can eventually progress to end-stage kidney disease and kidney failure. The only treatment options for kidney failure are dialysis or a kidney transplant.

Signs and Symptoms of C3 Glomerulopathy

Your kidneys are your body’s cleaning crew — they filter out toxins from your blood so these unwanted substances can be excreted in your urine. But did you know the kidneys have several other functions? These organs also maintain your body’s fluid balance, release hormones that help regulate your blood pressure, and even support your bone health.

Your kidney health has a direct impact on your overall health, so if your kidneys become damaged from C3G, you may develop symptoms or notice signs that they’re not working as well as they should. Symptoms vary from person to person, and they can be mild or severe depending on the amount of damage.

For many people, symptoms aren’t noticeable until their C3G has progressed to a more advanced stage. C3G can develop at any age, but signs of DDD tend to show up earlier — usually in teenagers — compared with signs of C3GN. The median age of diagnosis for C3G is 23 years.

It’s important to note that if you don’t have a diagnosis and you experience the issues discussed below, you’re more likely to have another kidney-related condition, not C3G. This is because C3G is so rare. However, understanding these signs and symptoms may motivate you to get an evaluation by your doctor, which could lead to a diagnosis. Whether or not that diagnosis is C3G, understanding the following kidney-related issues can be an important first step.

1. Blood in Your Urine

Your urine can tell you a lot about your kidney health. If your urine appears red, pink, or brown, it may be a sign of C3G. These color changes are all caused by blood in your urine, also known as hematuria. You may also notice spots of blood floating in the toilet after you urinate. It’s also possible to have a very small amount of blood in your urine that can be detected only through urinalysis (a urine test), in which a sample is looked at under a microscope.

Hematuria is a sign that your kidney’s filtering units are damaged. Normally, the glomeruli filter out fluid, waste, and other substances from your blood over a thin membrane. This barrier keeps proteins and blood cells from leaving your body in your urine. However, in C3G, the glomeruli are damaged, allowing blood to leak out and be excreted from your body.

2. Dark, Foamy Urine

Dark, foamy, or cloudy urine may be a sign that protein is leaking into your urine as well. When your kidneys filter your blood, the proteins are too big to be excreted and are returned to your bloodstream. Proteins are essential building blocks for your muscles, and they also help your body reabsorb fluid to maintain balance.

In C3G, proteins can leak out of your kidneys and into your urine. This condition is known as proteinuria or albuminuria, referring to the protein albumin that can leak into urine as a result of kidney disease.

If your urine protein levels are extremely high, you may have a condition known as nephrotic syndrome. Other symptoms associated with this glomerular disease include loss of appetite, swelling, and weight gain from excess fluid buildup in your body.

3. Fatigue and Trouble Concentrating

Damaged kidneys can’t properly filter out wastes and toxins from your blood, causing these substances to build up. This condition is known as uremia, or “urea in the blood.” It causes increased levels of creatinine (a breakdown product made from muscle cells) and urea (waste made by the liver after it breaks down proteins).

Uremia may be a sign of C3G or its progression to more severe disease. The buildup of creatinine and urea in your blood can interfere with your brain’s functioning, making it difficult to remember things or concentrate. Fatigue, muscle cramps, itching, and shortness of breath are also common symptoms of uremia.

4. Swollen Hands and Feet

As C3G progresses, you may start to notice symptoms of more severe disease, including edema (swelling). Your kidneys can’t clear out excess fluid as well as before, so the fluid begins collecting in your body. Albumin helps balance your body’s fluid levels — proteinuria in C3G reduces the amount of protein in your blood, interfering with this balance.

You may notice swollen, shiny, or tight-feeling skin around your hands, feet, and ankles. The skin around your eyes can also become puffy, making your lids and the area underneath your eyes look swollen.

5. Gout

Uric acid, a product made from breaking down purines (substances found in alcohol and certain foods), is typically filtered out by your kidneys and excreted in your urine. In C3G, your kidneys can’t remove enough uric acid, so it begins collecting in your joints and crystallizing. This is known as gout, a type of inflammatory arthritis that causes painful, swollen, hot joints.

Gout typically affects one joint at a time, most often the big toe. However, it can also involve the other toe joints, knees, or ankles. Gout is a condition with periods of worsening symptoms (flares) and periods of relief (remission). Flares can last several days to weeks, depending on how severe your case is.

6. High Blood Pressure

Excess fluid buildup can put extra pressure on your blood vessels, causing high blood pressure. Also known as hypertension, high blood pressure is a common symptom of C3G and other kidney diseases. It’s important to address and treat it before it damages your kidneys further.

You probably won’t notice any symptoms of high blood pressure, so it’s important to get regular checkups and screenings at your doctor’s office. Some people experience headaches, nosebleeds, or shortness of breath with high blood pressure, but only in severe cases.

Talk to Your Doctor About Your Symptoms

If you’ve noticed new symptoms of C3G or if they’ve become worse recently, talk to your doctor or nephrologist. It’s important to keep them updated on your symptoms not only at your first appointment but also at every visit.

Worsening symptoms may be a sign that your current treatment plan isn’t as effective as it should be. Your doctor or nephrologist may change one or more of your medications to better manage your symptoms and prevent C3G from progressing into more severe kidney disease.

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At MyKidneyDiseaseCenter, the site for people with kidney disease and their loved ones, people come together to gain a new understanding of kidney disease and share their stories with others who understand life with kidney disease.

Are you living with C3 glomerulopathy? What symptoms have you noticed? Share your experiences in the comments below.