Synonyms:

• CH₅₀
• Total Hemolytic Complement

The Complement, Total (CH50) blood test is used to evaluate and follow up SLE (systemic lupus erythematosus) patient’s response to therapy; may predict disease flare in SLE; evaluate for complement component deficiency; evaluate complement activity in cases of immune complex disease, glomerulonephritis, rheumatoid arthritis, SBE, cryoglobulinemia. The CH₅₀ assay mainly evaluates the classical pathway.

Complement is a system of 25 cell membrane associated and plasma proteins, which when activated produce multiple inflammatory mediators, opsonins, lysins, and down regulators vital to the normal function of the immune system. Complement components belong to a ”classical” and ”alternative” pathway whose activation steps differ. Complement proteins can be increased as part of the acute phase response to inflammation or infection, and they can be decreased or absent due to hypercatabolism, expenditure in immune complexes, or hereditary deficiency. Patients with hereditary absence of a complement protein may have decreased total complement and recurrent bacterial infections or a rheumatic illness. Conversely, patients with rheumatic diseases, particularly with active illness and activation of complement and formation of immune complexes, may have low total complement. Falling complement levels may presage clinical flares, particularly of lupus nephritis.