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Complement C4 Testing is used to quantify the level of C4 in the blood. Complement C4 is a glycoprotein that plays an important role in the activation of Classical Complement Pathway.

This test is used to detect those individuals who have inborn (present at birth) deficiency of this complement or those with immunologic disease in whom hypercatabolism of complement causes reduced levels. Examples of these diseases include serum sickness, lupus erythematosus, chronic active hepatitis, and certain glomerulonephritides. If a significant deviation from the normal range is noticed, further evaluation may be required.