Complement deficiencies
Recognising inherited and acquired complement deficiency from the clinical pattern (recurrent Neisseria, lupus, pyogenic infection, aHUS), screening with CH50 and AH50, and prevention with meningococcal vaccines, prophylaxis and family testing, including the infection risk of each complement inhibitor.
Tier 2Condition
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Complement deficiency is rare (a small minority of registered inborn errors of immunity; figures vary between registries) but the presentations are distinctive.
- The level of the block predicts the picture:
- early classical (C1q, C1r/s, C4, C2): lupus and encapsulated bacteria
- C3 and its regulators (factor H, factor I): severe pyogenic infection, aHUS, C3 glomerulopathy
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Sources
- Primary Immunodeficiencies (PID) Clinical UpdateAU/NZASCIA (Australasian Society of Clinical Immunology and Allergy), 2025
- Australian Immunisation Handbook: Meningococcal diseaseAU/NZAustralian Technical Advisory Group on Immunisation (ATAGI), Australian Government Department of Health, Updated 12 November 2026
- Human inborn errors of immunity: 2024 update on the classification from the International Union of Immunological Societies Expert Committee (Poli MC et al. J Hum Immun 2025;1(1):e20250003)International Union of Immunological Societies, 2024 update (published April 2025)
- Complement deficiencies and infections (El Sissy C et al. Curr Opin Immunol 2026;98:102711)Current Opinion in Immunology, 2026
- Infectious diseases associated with complement deficiencies (Figueroa JE, Densen P. Clin Microbiol Rev 1991;4:359-95)Clinical Microbiology Reviews, 1991
- High risk for invasive meningococcal disease among patients receiving eculizumab despite receipt of meningococcal vaccine (McNamara LA et al. MMWR 2017;66:734-7)US Centers for Disease Control and Prevention, 2017
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Deploy to Cloudflare on push to main