C4 Complement Blood Test

What is a C4 complement blood test?

A complement C4 blood test (or complement component 4 test) measures how much C4 protein you have in your blood. C4 proteins enhance your immune system so it can protect your body from bacteria and viruses. C4 is one of nine main complement proteins, which are labeled C1 through C9.

Information about your C4 levels can tell your healthcare provider how well your immune system is working. Low C4 levels mean you have a higher risk of developing an autoimmune condition or infection. High C4 levels can mean your body is recovering from an illness or that your body is responding well to treatment for an autoimmune disorder.

A C4 test involves providing a blood sample in your healthcare provider’s office or a lab.

When is a C4 complement blood test performed?

Your healthcare provider may recommend a C4 test if you have:

• Signs of an autoimmune disorder like lupus or rheumatoid arthritis (RA).
• Frequent bacterial or fungal infections.
• Muscle or joint pain.
• Swelling or inflammation.

Your healthcare provider might also recommend a C4 complement test to monitor if treatment for an autoimmune disorder is working.

How does a C4 complement test work?

Your healthcare provider takes a sample of your blood through a vein in your arm or hand. It takes just a few minutes. Then, they send the sample to a lab. Your healthcare provider will contact you with your results and explain what they mean.

What should I expect during a C4 complement test?

You don’t need to do anything to prepare for a complement blood test. Here’s how you can expect a C4 blood test to go:

1. A phlebotomist will locate a vein by wrapping an elastic band around your upper arm.
2. They’ll clean the area containing the vein with an antiseptic.
3. They’ll insert a needle into the vein. You may feel a sting.
4. They’ll remove the elastic band once blood starts to flow.
5. Your provider will collect a sample of your blood in a vial.
6. They’ll remove the needle.
7. Your healthcare provider will put a bandage over the area.

What should I expect after a C4 complement test?

You can resume your normal activities after a C4 complement blood test. A small bruise may form where the needle was in your skin.

What are the risks of a C4 complement test?

Blood draws are very safe and complications are rare. Possible risks include bleeding, fainting or infection.

What kind of results do I get from a C4 complement test?

You’ll get your C4 complement test results as a number in milligrams per deciliter (mg/dL). Generally, an acceptable range is 14 mg/dL to 45 mg/dL. Ask your healthcare provider what a normal range is for you.

What do low levels of C4 mean?

Low C4 protein levels can be a sign of:

• An autoimmune disease or that you’re at a higher risk of developing an autoimmune disorder.
• Recurring bacterial infections.
• Hemolytic anemia (AIHA).
• Hepatitis.
• Hereditary angioedema (swelling under the skin).
• Kidney disease.
• Cirrhosis.
• Malnutrition.

What do high levels of C4 mean?

High C4 protein levels may mean you’re recovering from an infection or illness. If you’re getting treatment for an autoimmune disease, high C4 typically means treatment is working.

High C4 levels may also be a sign of the following health conditions:

• Ulcerative colitis.
• Sarcoidosis (inflammatory disease).
• Certain types of cancer.

When should I know the C4 complement blood test results?

You can expect to get your test results within a few days. Your healthcare provider will contact you to discuss your results.

When should I call my healthcare provider?

Call your healthcare provider if you have questions about the results of your C4 complement blood test.