Measurement of C4 in serum is used to detect individuals with inborn deficiency of this factor or those with immunologic disease in whom complement is consumed at an increased rate. These include lupus erythematosus, chronic active hepatitis, certain chronic infections, post-streptococcal and membranoproliferative glomerulonephritis, and others.

SST. Minimum volume 1 (0.5) mL serum. Stability: Ambient – 72 Hours, Refrigerated – 7 Days, Frozen – 2 Months