COMPLEMENT C4, SERUM

Complement C4, Serum

What it is

The Complement C4, Serum test measures the level of complement component 4 (C4) in the blood. C4 is an essential protein in the complement system, which is part of the immune system that helps defend the body against infections, clear immune complexes, and trigger inflammation when needed.

Uses

This test is commonly used to evaluate immune system activity, especially in autoimmune and inflammatory disorders. It is often ordered along with C3 or as part of a full complement panel. It helps in diagnosing and monitoring conditions such as systemic lupus erythematosus (SLE), rheumatoid arthritis, vasculitis, and certain types of glomerulonephritis.

Symptoms That May Lead to the Test

Doctors may order this test if you have symptoms like joint pain and swelling, unexplained skin rashes (including butterfly rash in lupus), fever, fatigue, kidney-related symptoms (swelling, foamy urine, high blood pressure), or recurrent infections that suggest immune dysfunction.

Abnormal Results

Low C4 Levels: Often seen in autoimmune diseases like lupus, immune complex diseases, certain kidney conditions, or rare hereditary complement deficiencies.

High C4 Levels: May occur in acute inflammation, infections, metabolic conditions, and during pregnancy, reflecting increased immune activity.

Normal C4 Levels: Suggest no significant abnormalities in this component of the immune system, though further immune and complement testing may be required depending on clinical suspicion.

Risks

The test involves a routine blood draw, which carries minimal risks such as mild pain, slight bruising, or temporary dizziness at the puncture site. These effects are mild and usually resolve quickly.