What does a high C4 means?

A high C4 level typically refers to elevated levels of C4 complement protein in the blood, which can indicate an immune response or inflammation. C4 is part of the complement system, which aids in the body's defense against infections. Elevated C4 levels may be associated with autoimmune diseases, such as systemic lupus erythematosus, or certain infections, and can warrant further investigation by a healthcare professional to determine the underlying cause.