C3 Complement Blood Test

What is a C3 complement blood test?

A C3 complement blood test measures the levels of a specific type of protein in your blood (C3 proteins). C3 proteins are part of your complement system, which is connected to your immune system. C3 proteins destroy organisms that make you sick and they help heal your body after an illness. But sometimes, C3 proteins launch an attack against healthy cells by mistake.

The results of this blood test give your healthcare provider information about how your immune system is working. By measuring the amount of C3 proteins, your healthcare provider can diagnose infection, disease, immune deficiency and other health conditions, like autoimmune disorders. This test also helps your healthcare provider monitor treatment for certain autoimmune diseases.

When is a C3 complement blood test performed?

Your healthcare provider may order this test if you have:

• Bacterial infections that don’t go away or keep coming back.
• Edema (swelling) or inflammation.
• Symptoms of an autoimmune disorder, like lupus.

Your healthcare provider might also recommend a C3 complement blood test to monitor:

• Immune complex-related conditions, including glomerulonephritis (GN) and vasculitis.
• Treatments for autoimmune disorders, including lupus or rheumatoid arthritis (RA).

How does a C3 complement test work?

Your healthcare provider removes a sample of your blood through a vein in your arm. It takes just a few minutes. Then, they send the sample to a lab to check the levels of C3 proteins in your blood.

The lab may also look at the levels of other proteins (such as C4 proteins) and see how they compare to the amount of C3 proteins. Your healthcare provider will contact you when the results are ready and explain what they mean.

What should I expect during a C3 complement test?

You don’t need to do anything to prepare for a C3 complement blood test. Here’s how you can expect a C3 test to go:

1. A phlebotomist will wrap an elastic band around your elbow to locate a vein in your inner arm or hand.
2. They clean the area with antiseptic.
3. They insert a needle into the vein. You may feel a sting or pinch from the needle.
4. Your provider collects a sample of your blood in a tube.
5. They remove the needle.
6. Your healthcare provider will tape some gauze to your arm where the needle was.

What should I expect after a C3 complement test?

Your arm may be sore for several hours, and you may get a small bruise on your vein.

What are the risks of a C3 complement test?

Blood tests are very safe, and they give your healthcare provider important information. There aren’t any risks of a C3 blood test. If you don’t like having to give a blood sample or feel faint after giving blood, let the phlebotomist know.

What kind of results do I get from a C3 complement test?

You’ll likely get your test results as a number in milligrams per deciliter (mg/dL) or grams per liter (g/L). The normal range of C3 proteins varies depending on age, sex and overall health. A normal range is usually between 80 and 178 mg/dL or 0.8 and 1.7 g/L. Ask your healthcare provider what the normal range is for you and your laboratory.

What do low levels of C3 mean?

If you don’t have enough C3, you may be more likely to develop certain diseases or infections. Lower-than-normal levels of C3 proteins can be a sign of:

• Autoimmune diseases like psoriatic arthritis, Crohn’s disease, lupus or rheumatoid arthritis, or that you’re at a higher risk of developing an autoimmune disorder.
• C3 deficiency, which leads to recurring bacterial infections.
• Hemolytic anemia (AIHA).
• Hepatitis (inflammation of the liver), most often hepatitis A, hepatitis B or hepatitis C.
• Hereditary angioedema (swelling under the skin).
• Infections, especially bacterial infections and those that result from parasites (including malaria).
• Kidney disease/chronic kidney disease.
• Liver disease.
• Malnutrition.
• Organ rejection, such as kidney transplant rejection.
• Septicemia (blood poisoning).

What do high levels of C3 mean?

Higher-than-normal levels of C3 proteins can indicate that your immune system is responding to a recent infection. If you’re getting treatment for lupus or another autoimmune disease, higher levels of C3 proteins usually mean that treatment is working.

Increased C3 levels may also be a sign of the following health conditions:

• Heart attack (myocardial infarction) and other heart problems.
• Sarcoidosis (inflammatory disease).
• Some types of cancer.
• Thyroid disease.
• Ulcerative colitis.

When should I know the C3 complement blood test results?

Results from this test are usually ready in a few days. But it can also take up to a week for them to be ready. Your healthcare provider will contact you to discuss the results.

When should I call my doctor?

Call your healthcare provider if you:

• Have any questions about the results of your C3 complement blood test.
• Have bleeding or pain from where the needle was in your arm for the blood test.