Table 1. Etiologies of Complement-Mediated Thrombotic Microangiopathies.

Etiology	Mechanism
Genetic mutations in complement regulators: (e.g., CFH, CFI, MCP/CD46, C3, CFB)	Lead to loss of control over the alternative complement pathway, resulting in excessive complement activation, endothelial injury, and microvascular thrombosis
Acquired autoantibodies (e.g., anti-factor H)	Autoantibodies inhibit function of complement regulatory proteins, causing unrestrained complement activation and endothelial damage
Pregnancy	Increased complement activation triggering disease
Infections (e.g., influenza, HIV)	Trigger for complement overactivation
Surgery or trauma	Systemic inflammation and complement activation
Certain medications (e.g., calcineurin inhibitors)	Drug-induced endothelial injury
Transplantation	Immunological stress and complement activation

HIV: human immunodeficiency virus.