Home Anti–Factor H Autoantibodies and ELISA Testing: Optimizing Diagnosis in Atypical Hemolytic Uremic Syndrome (aHUS)

This is a close-up shot of a scientist or lab technician at work. The person, wearing a white lab coat and blue disposable gloves, is holding a 96-well microplate containing a blue liquid. With their other hand, they are using a micropipette to carefully dispense a sample into one of the wells, suggesting a scientific experiment or analysis is in progress.

02.02.2026

Anti–Factor H Autoantibodies and ELISA Testing: Optimizing Diagnosis in Atypical Hemolytic Uremic Syndrome (aHUS)

Atypical hemolytic uremic syndrome (aHUS), also known as complement-mediated thrombotic microangiopathy (CM-TMA), is a rare but life-threatening condition caused by dysregulation of the alternative complement pathway. Among the known etiologies, autoantibodies against complement factor H (anti-factor H) play a critical role, accounting for approximately 10% of cases¹. Accurate laboratory detection of these antibodies is essential, as it directly impacts diagnosis, prognosis, and therapeutic strategies.

Why Anti-Factor H Antibody Testing Is Clinically Relevant

Patients with anti-factor H antibodies often benefit from targeted immunosuppressive therapies, such as corticosteroids or rituximab, in addition to plasma exchange. Early and reliable identification of anti-factor H immunoglobulin G (IgG) is therefore crucial to preventing irreversible organ damage, particularly renal failure. The ELISA assay is the reference method for detecting and quantifying anti-factor H in clinical laboratories.

However, the increasing availability of commercial kits raises important questions regarding assay comparability, sensitivity, specificity, and standardization.

Comparing ELISA Assays for Anti-Factor H Autoantibodies

A recent Canadian study compared three ELISA methods for anti-factor H antibodies detection²:

a validated in-house ELISA based on the Paris protocol,
a commercial ELISA from GA Generic Assays,
and a second commercially available ELISA kit.

A total of 75 plasma samples from patients with suspected aHUS were analyzed in parallel. The study evaluated qualitative agreement, quantitative correlation, and analytical performance under routine diagnostic conditions.

Key Findings: Sensitivity, Specificity, and Concordance

All assays demonstrated good performance in identifying negative samples. However, differences emerged in positive samples and antibody quantification:

The ELISA from GA Generic Assays showed the highest concordance with the in-house reference method. It exhibit good sensitivity, as well as strong quantitative correlation and reproducibility.
The second commercial assay displayed greater variability, particularly at higher antibody titers, and tended to underestimate anti-factor H concentrations.
Applying manufacturer-defined cut-offs alone increased the risk of false-negative results. However, adjusting positivity thresholds based on laboratory-specific healthy controls (e.g., mean + 2 SD) significantly improved diagnostic sensitivity with minimal loss of specificity.

These findings confirm that ELISA assays for anti-factor H antibodies are not interchangeable, especially for patient monitoring and longitudinal follow-up.

Practical Implications for Diagnostic Laboratories

The study highlights several best practices for laboratories performing anti-Factor H antibody testing:

Use optimized cut-off values tailored to the tested population, as recommended also by the International Organization for Standardization (ISO) 15189 standard for clinical laboratory accreditation³.
Include individual blank controls to reduce false positives caused by non-specific binding.
When clinically relevant, confirm positive results with a second ELISA method to support treatment decisions.
Be aware that ELISA assays detect only free circulating antibodies, potentially missing immune-complexed anti-factor H.

Conclusion

This image is a detailed digital illustration of the human abdominal and thoracic organs, rendered in a stylized, glowing X-ray or thermal view. The central focus is on the two prominent, bean-shaped kidneys, which are highlighted in a bright, glowing red. These are located on either side of the spine, below the liver and stomach. The surrounding organs are shown in a translucent blue outline, which includes: The liver and stomach in the upper part of the abdomen. The large and small intestines in the lower part. The lungs and parts of the rib cage are also visible in the upper torso.The overall impression is a visualization of the human anatomy, specifically highlighting the position and structure of the kidneys in relation to other internal organs.

Reliable detection of anti-factor H autoantibodies is essential for modern diagnostics of atypical hemolytic uremic syndrome (aHUS). Although commercial ELISA kits provide accessible and standardized solutions, their analytical performance varies. Evidence supports using well-validated ELISA assays, such as Anti-Factor H from GA Generic Assays, in conjunction with thoughtful interpretation of results and laboratory-specific validation.

Optimizing ELISA testing for anti-factor H antibodies can lead to earlier diagnosis, more precise therapy, and improved outcomes for patients with aHUS and related complement disorders.