Test Details: CH 50 test is a complement blood test that measures the amount or activity of complement proteins in the blood. There are nine major complement proteins from C1-C9. Complement proteins may be measured individually or together. C3 and C4 proteins are the most commonly tested individual complement proteins. CH50 test measures the amount and activity of all major complement proteins. Decreased levels are seen in autoimmune disorders while increased levels in malignant conditions.