Complement C4(C4) Determination Reagent(Immunoturbidimetry) is an in vitro diagnostic quantitative test kit. Quantitation of C4 is used to detect individuals with inborn deficiency of this factor or those with immunologic disease in whom hypercatabolism of complement causes reduced levels. These diseases include lupus erythematosus, serum sickness, certain glomerulonephritides, chronic active hepatitis, and others.