Enzyme-Linked Immunosorbent Assay (ELISA)
Antibody Factor H
Anti-Complement Factor H
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
1. Immediately after specimen collection, place the tube on wet ice.
2. Centrifuge and aliquot serum into plastic vial.
3. Freeze specimen within 30 minutes.
Additional Information: If the specimen is to be shared with AHUSD / Atypical Hemolytic Uremic Syndrome Complement Panel, Serum and Plasma, only serum collected in a red-top tube is acceptable.
|Specimen Type||Temperature||Time||Special Container|
|Serum Red||Frozen (preferred)||28 days|
AFH are found in 6% to 10% of aHUS patients, and the presence or absence of AFH can be a determinant of whether immunosuppressive therapy is warranted versus complement-blocking therapy.(1) Deletion of the CFHR1 gene, with or without other CFHR genes, can result in predisposition to generation of AFH; however, not all individuals with CFHR1 deletion develop AFH, and conversely, some individuals with the autoantibody do not have a CFHR1 deletion.(2) Most commonly, the deletion encompasses both the CFHR1 and CFHR3 genes. The allele frequency of the CFHR3/CFHR1 deletion varies among populations, from 0% in Japanese and South American populations to 54.7% in Nigeria; similarly, the frequency of homozygosity for the deletion ranges from 0% up to 33% in Nigeria.(3) Interestingly, while AFH are much more common in aHUS cohorts from India, accounting for approximately 50% of cases, the population frequency of homozygous CFHR1 deletion is 9.5%, which is not significantly higher than in other populations.(4,5) The mechanism that results in AFH formation in the presence of the deletion remains unknown. Most of the autoantibodies inhibit FH function by binding and blocking the C-terminus, impairing its ability to bind endothelial cell surfaces, sialic acids, and C3b; however, in some individuals, the AFH may recognize other regions, such as the N-terminal SCR1-4.
Absent (<15.8 U/mL): Antibodies to factor H are not detected.
Present (> or =15.8 U/mL): Antibodies to factor H are detected. Clinical correlation recommended.
Healthy individuals may see false-positive results for anti-factor H (AFH) since the diseases where AFH is pathogenic are so rare.
Positive AFH results can occur in healthy individuals and in IgA nephropathy. AFH could be an incidental finding in patients with diseases other than atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathies (C3G). This is most likely due to the multifactorial nature of the diseases and differences in penetrance for genetic variants.
Results should be interpreted in the context of other complement assays and other laboratory tests in the evaluation of thrombotic microangiopathies or C3G.
Use of caution is suggested on a finding of AFH in the clinical setting.
This assay to measure AFH is not standardized to European methods and results obtained by other laboratories can only be compared qualitatively.
1. Ekdahl KN, Persson B, Mohlin C, Sandholm K, Skattum L, Nilsson B: Interpretation of serological complement biomarkers in disease. Front Immunol. 2018 Oct 24;9:2237. doi: 10.3389/fimmu.2018.02237
2. Jozsi M, Licht C, Strobel S, et al: Factor H autoantibodies in atypical hemolytic uremic syndrome correlate with CFHR1/CFHR3 deficiency. Blood. 2008 Feb 1;111(3):1512-1514. doi: 10.1182/blood-2007-09-109876
3. Holmes LV, Strain L, Staniforth SJ, et al: Determining the population frequency of the CFHR3/CFHR1 deletion at 1q32. PLoS One. 2013 Apr 16;8(4):e60352. doi: 10.1371/journal.pone.0060352
4. Sinha A, Gulati A, Saini S, et al: Prompt plasma exchanges and immunosuppressive treatment improves the outcomes of anti-factor H autoantibody-associated hemolytic uremic syndrome in children. Kidney Int. 2014 May;85(5):1151-1160. doi: 10.1038/ki.2013.373
5. Durey MA, Sinha A, Togarsimalemath SK, Bagga A: Anti-complement-factor H-associated glomerulopathies. Nat Rev Nephrol. 2016 Sep;12(9):563-578. doi: 10.1038/nrneph.2016.99
6. Blanc C, Togarsimalemath SK, Chauvet S, et al: Anti-factor H autoantibodies in C3 glomerulopathies and in atypical hemolytic uremic syndrome: one target, two diseases. J Immunol. 2015 Jun 1;194(11):5129-5138. doi: 10.4049/jimmunol.1402770
7. Zhang Y, Ghiringhelli Borsa N, Shao D, et al: Factor H autoantibodies and complement-mediated diseases. Front Immunol. 2020 Dec 15;11:607211. doi: 10.3389/fimmu.2020.607211
8. Sanchez-Corral P, Pouw RB, Lopez-Trascasa M, Jozsi M: Self-damage caused by dysregulation of the complement alternative pathway: Relevance of the factor H protein family. Front Immunol. 2018 Jul 12;9:1607. doi: 10.3389/fimmu.2018.01607
9. Dragon-Durey MA, Blanc C, Roumenina LT, et al: Anti-factor H autoantibodies assay. Methods Mol Biol. 2014;1100:249-56. doi: 10.1007/978-1-62703-724-2_20
The anti-factor H enzyme-linked immunoassay assay for the quantitation of antibodies to complement factor H is a 3-step procedure. In the first step, standards, controls, and diluted patient specimens are incubated with human recombinant complement factor H immobilized on a microwell plate. During this incubation, antibodies to factor H (AFH) present in the standards, controls, and patient sample will bind to the factor H-coated microwell plate. After incubation, a wash cycle removes the unbound material. In the second step, anti-human IgG conjugated to horseradish peroxidase (HRP) is added to the wells and incubated. The conjugate reacts with the AFH bound to the microwell plate. After incubation, a wash cycle removes the excess conjugate. In the third step, a chromogenic enzyme substrate is added to the wells and incubated. The bound HRP-conjugate reacts with the substrate forming a blue color. The enzyme reaction is stopped by dispensing an acidic solution into the wells, changing the color of the solution from blue to yellow. The color intensity of the reaction mixture is measured spectrophotometrically at 450 nm and is directly proportional to the amount of AFH present in the patient specimens, standards, and controls.(Package insert: Anti-Faktor H. GA Generic Assays GmbH; 11/2015)
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
|Test Id||Test Order Name||Order LOINC Value|
|AFH||Factor H Autoantibody, S||In Process|
|Result Id||Test Result Name||
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|AFH||Factor H Autoantibody, S||In Process|