The C4 and C3 complement blood tests are laboratory tests that measure the levels of two complement proteins in the blood. Complement proteins are part of the body’s immune system and play a role in defending against infections and other threats to the body.

C3 and C4 complement proteins are produced by the liver and circulate in the blood. Low levels of these proteins may indicate a deficiency in the complement system, which can increase the risk of infections and other immune-related diseases.

The C3 complement test measures the level of C3 protein in the blood. The normal range for C3 levels in the blood is between 90 and 180 milligrams per deciliter (mg/dL). Elevated levels of C3 may be associated with certain autoimmune diseases, such as lupus and rheumatoid arthritis.

The C4 complement test measures the level of C4 protein in the blood. The normal range for C4 levels in the blood is between 10 and 40 mg/dL. Low levels of C4 may be associated with certain autoimmune diseases, such as lupus, and may also indicate a deficiency in the complement system.

Both C3 and C4 complement tests are often used in combination to diagnose and monitor autoimmune diseases, such as lupus, and to evaluate the effectiveness of treatment. In some cases, other tests may be ordered to confirm a diagnosis or determine the specific type of autoimmune disease present.

The C3 and C4 complement blood tests are simple procedures that involve taking a small sample of blood from a vein in the arm. The samples are then sent to a laboratory for analysis. Results are usually available within a few days.

In summary, the C3 and C4 complement blood tests are useful tools in the diagnosis and monitoring of autoimmune diseases and complement deficiencies. If you have symptoms of an autoimmune disease or are at risk of developing one, talk to your healthcare provider about whether these blood tests may be appropriate for you.