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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Clinical Immunology · Complement Factor I Deficiency

Building Your Care Team and Preparing for Visits

At a Glance

People with complete complement factor I deficiency benefit from coordinated care led by an immunologist or infectious disease specialist. Bring original genetic, complement, vaccination, and kidney records, and keep an emergency card ready for urgent infection evaluation.

Because complete Complement Factor I (CFI) deficiency can affect multiple systems in the body, care is rarely managed by a single doctor. Managing an ultrarare disease requires a collaborative, multidisciplinary team—a group of specialists who communicate to protect you from infection while monitoring your overall health [1][2].

Establishing this team early helps move care from a “reactive” state of managing emergencies to a “proactive” state of maintaining long-term wellness [3].

Your Collaborative Medical Team

Care for CFI deficiency should be highly individualized. Depending on your symptoms and test results, your team may include:

  • Clinical Immunologist / Infectious Disease Specialist: These specialists often lead the diagnostic process (confirming complete deficiency through functional and genetic testing) and design your individualized infection-prevention plan, including vaccinations and prophylactic antibiotics [1][2].
  • Primary Care Provider / Pediatrician: The foundational clinician who manages routine health, coordinates referrals, and often serves as the first point of contact for acute illnesses.
  • Genetic Counselor: Essential for helping families interpret complex CFI sequencing results, understanding reproductive risks, and coordinating cascade testing for siblings or other relatives [1][4].
  • Nephrologist (Kidney Specialist): Because of the potential risks for complement-mediated kidney complications (like aHUS or C3G), a nephrologist may be involved to establish baseline kidney function and monitor for signs of inflammation [5][6].
  • Ophthalmologist: Recommended for baseline and individualized periodic screening of the retina to watch for early signs of complement-mediated eye changes [7][8].
  • Rheumatologist or Neurologist: Involvement from these specialists is not routine but may be requested if specific, rare systemic symptoms (like unexplained rashes, joint pain, or severe neurological changes) occur [1][9].

First Visit Checklist: What to Bring

When establishing care, specialists need “raw data,” not just a summary of your history. Bring physical or digital copies of the following artifacts:

  1. The Full Genetic Report: This must include the specific variants found, whether they are biallelic (homozygous or compound heterozygous), and whether specialized testing like MLPA was performed [1][10].
  2. Original Complement Labs: Bring the actual lab printouts for C3, C4, CH50, and AP50 [4][11]. Most importantly, bring the Factor I functional assay results [12][13].
  3. Vaccination Records: A complete list of every vaccine given, including the specific brand and the dates of every dose [2][14].
  4. Renal Baseline Data: Your most recent results for creatinine/eGFR, urinalysis, and blood pressure readings [15][6].
  5. An Emergency Care Plan: Work with your team to create a printable emergency card containing your confirmed diagnosis, baseline complement results, medication/allergy list, treating-team contacts, and explicit instructions that empiric evaluation for infection must not be delayed.

Having these documents ready allows your specialist to spend the visit discussing your care plan rather than searching for missing information. If possible, establishing care or consulting with a center that has specific experience in complement-mediated diseases is highly recommended [2][16].

Common questions in this guide

Which doctors usually care for someone with complete CFI deficiency?
A clinical immunologist or infectious disease specialist often leads care, while a primary care clinician coordinates routine health needs. A genetic counselor, nephrologist, and ophthalmologist may also be involved, with rheumatology or neurology added when specific symptoms require them.
What records should I take to my first CFI deficiency appointment?
Bring the full genetic report, including the exact variants, whether they affect both copies of the gene, and whether MLPA was performed. Also bring original C3, C4, CH50, AP50, and Factor I functional assay results, vaccination records, recent creatinine/eGFR, urinalysis and blood pressure results, and any emergency care plan.
Why does my CFI function test matter if my Factor I protein level was measured?
A Factor I functional assay shows how well the protein works, while an antigen test measures how much protein is present. Your specialist may use both results, along with genetic testing and other complement labs, to confirm complete deficiency and guide care.
What should be included in an emergency card for CFI deficiency?
The card should state the confirmed diagnosis, baseline complement results, medications and allergies, and contact details for the treating team. It should also tell emergency clinicians that evaluation for infection must not be delayed.
Should my siblings or other relatives get genetic testing for CFI deficiency?
A genetic counselor can review the family’s CFI results, explain reproductive considerations, and coordinate cascade testing for siblings or other relatives. Testing decisions should be based on the family’s results and discussed with a qualified clinician.
How do kidney and eye monitoring fit into CFI deficiency care?
A nephrologist may establish baseline kidney function and monitor for inflammation or complement-related kidney disease, while an ophthalmologist may arrange baseline and periodic retinal checks. The timing of monitoring should be individualized according to symptoms and test results.

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References

References (16)
  1. 1

    Complete Complement Factor I (CFI) deficiency: a systematic review of forty-nine patients including three novel cases.

    Rajabi E, Kheirabadi MC, Olyaei NA, et al.

    BMC immunology 2025; (26(1)):54 doi:10.1186/s12865-025-00739-y.

    PMID: 40713518
  2. 2

    Inherited Classical and Alternative Pathway Complement Deficiencies in Children: A Single Center Experience.

    Genel F, Erdem SB, Gülez N, et al.

    Iranian journal of immunology : IJI 2018; (15(4)):309-320 doi:10.22034/IJI.2018.39400.

    PMID: 30593745
  3. 3

    Early Versus Late Diagnosis of Complement Factor I Deficiency: Clinical Consequences Illustrated in Two Families with Novel Homozygous CFI Mutations.

    Franco-Jarava C, Álvarez de la Campa E, Solanich X, et al.

    Journal of clinical immunology 2017; (37(8)):781-789 doi:10.1007/s10875-017-0447-x.

    PMID: 28942469
  4. 4

    Cutaneous Vasculitis and Recurrent Infection Caused by Deficiency in Complement Factor I.

    Nanthapisal S, Eleftheriou D, Gilmour K, et al.

    Frontiers in immunology 2018; (9()):735 doi:10.3389/fimmu.2018.00735.

    PMID: 29696024
  5. 5

    Complement Factor I Gene Variant in an Atypical Hemolytic Uremic Syndrome Triggered by Hypereosinophilia Syndrome.

    Banjongjit A, Kittanamongkolchai W, Kanjanabuch T

    Nephron 2023; (147(11)):701-706 doi:10.1159/000531879.

    PMID: 37611541
  6. 6

    A novel missense mutation in complement factor I predisposes patients to atypical hemolytic uremic syndrome: a case report.

    Wei X, Li J, Zhan X, et al.

    Journal of medical case reports 2022; (16(1)):101 doi:10.1186/s13256-022-03312-y.

    PMID: 35241161
  7. 7

    Rare Dysfunctional Complement Factor I Genetic Variants and Progression to Advanced Age-Related Macular Degeneration.

    Seddon JM, Rosner B, De D, et al.

    Ophthalmology science 2023; (3(2)):100265 doi:10.1016/j.xops.2022.100265.

    PMID: 36909148
  8. 8

    Geographic Atrophy in Patients with Age-Related Macular Degeneration Is Associated with Rare Variants in Complement Factor H and Complement Factor I.

    de Breuk A, de Jong S, Bakker B, et al.

    Ophthalmology science 2026; (6(6)):101171 doi:10.1016/j.xops.2026.101171.

    PMID: 42222588
  9. 9

    CNS Inflammation as the First Sign of Complement Factor I Deficiency: A Severe Myelitis Treated With Intense Immunotherapy and Eculizumab

    Massey V, Nguyen CE, François T, et al.

    Neurology(R) neuroimmunology & neuroinflammation 2024; (11(2)):e200191 doi:10.1212/NXI.0000000000200191.

    PMID: 38134378
  10. 10

    Functional evaluation of rare variants in complement factor I using a minigene assay.

    Donelson CJH, Ghiringhelli Borsa N, Taylor AO, et al.

    Frontiers in immunology 2024; (15()):1446081 doi:10.3389/fimmu.2024.1446081.

    PMID: 39238643
  11. 11

    Disseminated gonococcal infection secondary to a rare homozygous mutation resulting in complement factor I deficiency.

    Almpani M, Welch G, Vanderleeden E, et al.

    Journal of human immunity 2025; (1(3)):e20250088 doi:10.70962/jhi.20250088.

    PMID: 41607490
  12. 12

    Complement factor I deficiency: A potentially treatable cause of fulminant cerebral inflammation.

    Altmann T, Torvell M, Owens S, et al.

    Neurology(R) neuroimmunology & neuroinflammation 2020; (7(3)) doi:10.1212/NXI.0000000000000689.

    PMID: 32098865
  13. 13

    Functional Analysis of Rare Genetic Variants in Complement Factor I (CFI) using a Serum-Based Assay in Advanced Age-related Macular Degeneration.

    Java A, Baciu P, Widjajahakim R, et al.

    Translational vision science & technology 2020; (9(9)):37 doi:10.1167/tvst.9.9.37.

    PMID: 32908800
  14. 14

    Screening for Immunodeficiencies in Children With Invasive Pneumococcal Disease: Six-year Experience From a UK Children's Hospital.

    Bijker EM, Bateman EAL, Trück J, et al.

    The Pediatric infectious disease journal 2022; (41(7)):575-578 doi:10.1097/INF.0000000000003554.

    PMID: 35421038
  15. 15

    A young woman with membranoproliferative glomerulonephritis and persistent hypocomplementemia: a case report.

    Li H, Jinpu L, Lan L, et al.

    BMC nephrology 2026; (27(1)).

    PMID: 41764449
  16. 16

    Inherited defects in the complement system.

    Leonardi L, La Torre F, Soresina A, et al.

    Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology 2022; (33 Suppl 27()):73-76 doi:10.1111/pai.13635.

    PMID: 35080299

This page is for informational purposes only and does not constitute medical advice. Your immunologist and other specialists should tailor testing, infection prevention, monitoring, and emergency instructions to your situation.

Guide contents Immunodeficiency with factor I anomaly
Research & Literature
05 Protecting Your Health 07 Your Long-Term Outlook