SC5b-9

Elevated soluble C5b-9 (SC5b-9) levels indicate recent or ongoing activation of the complement system, while normal or reduced levels suggest no excessive activation. High SC5b-9 concentrations are associated with transplant-associated thrombotic microangiopathy (TA-TMA), a complication of hematopoietic stem cell transplants. Increased SC5b-9 may also occur in various conditions involving primary or secondary complement activation, such as immune-complex disease, infection, atypical hemolytic uremic syndrome, and C3 glomerulopathies. Due to a low specificity for SC5b-9 testing, results should be interpreted in combination with other clinical and laboratory evidence of disease activity. Plasma SC5b-9 levels may be used to monitor the efficacy of complement inhibitor drugs, as elevated levels suggest insufficient complement blockage to effectively prevent the formation of the terminal attack complex.