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C3 concentrations can be normal in patients with C3 glomerulopathy secondary to C3 nephritic factor
  1. Hamish Anderson,
  2. Mark Van Voorthuizen,
  3. John O'Donnell,
  4. Sarah Beck
  1. Immunology, Te Whatu Ora—Health New Zealand Canterbury Health Laboratories, Christchurch, New Zealand
  1. Correspondence to Dr Hamish Anderson, Immunology, Te Whatu Ora Health New Zealand Waitaha Canterbury, Christchurch, New Zealand; hamish.anderson{at}


C3 glomerulopathy (C3G) is a rare kidney disease caused by the glomerular deposition of C3 fragments secondary to alternative pathway complement dysregulation. C3 nephritic factors (C3Nef) are the most common acquired cause, and their detection has treatment and prognostic implications. Although C3 concentration can be normal in the presence of C3Nef, many laboratories will only perform C3Nef testing when C3 is low. We performed a retrospective study of all positive C3Nef results from the authors’ laboratory since 2015 and found that two of the four patients with positive C3Nef and biopsy-confirmed C3G had normal C3 concentrations. This may be in part due to limitations in commercial C3 testing methods which use anti-C3c antisera directed against both C3 breakdown products and native C3. A normal C3 concentration should not preclude C3Nef testing in the appropriate clinical context.

  • Complement System Proteins
  • Allergy and Immunology
  • Autoantibodies

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  • Handling editor Patrick J Twomey.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.