Synonyms

   4th Component of Complement

Clinical Significance

   It is useful for Investigating an undetectable total complement (CH50), Confirming hereditary angioedema (with low C1 inhibitor) and Assessing disease activity in systemic lupus erythematosus, proliferative glomerulonephritis, rheumatoid arthritis, and autoimmune hemolytic anemia.

Specimen

   Serum

Stability

   Refrigerated (preferred) : 7 days

   Frozen : 28 days

   Ambient : 72 hours

Reference Range

   0.16 – 0.6 g/L

Interpretation

   C4 levels will be decreased in acquired autoimmune disorders, in active phase of lupus erythematosus, and in rheumatoid arthritis. An undetectable C4 level (with normal C3) suggests a congenital C4 deficiency. Levels will be increased in patients with autoimmune hemolytic anemia.