Analytical performance of new Optilite® C1q and C2 turbidimetric immunoassays and clinical performance in inherited and acquired complement abnormalities
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Updated: Oct 31, 2026
Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
Published on: January 29, 2014
Victor Iliev1, Jake D Fisher2, Iasmina A Gavrilas2
1The Binding Site, part of Thermo Fisher Scientific, Birmingham, UK..
Background:
Quantitative complement assessment, alongside classical pathway functional complement (CH50) testing, is essential for diagnosing complement deficiencies and complement-mediated disorders. We developed two new automated turbidimetric immunoassays, the Optilite® C1q and C2, validated their analytical performance, and evaluated their clinical utility in patients with complement-mediated renal diseases and complement deficiencies.
Methods:
We assessed the analytical performance of the C1q and C2 immunoassays using native and surrogate patient samples according to relevant CLSI guidelines. Reference ranges were determined using samples from healthy European donors. C1q and C2 results were compared with available CH50, C3 and C4 data in C3 glomerulopathy (C3G; n = 46), atypical haemolytic uremic syndrome (aHUS; n = 18), and inherited complement deficiency (n = 23) cohorts.
Results:
Optilite C1q and C2 immunoassays demonstrated robust analytical performance with total precision of 2.5-3.8% CV and 4.9-5.7% CV for C1q and C2, respectively. Reference ranges were 119.77-195.76 mg/L for C1q and 10.589-23.932 mg/L for C2. Assays showed strong agreement with established methods (87.3% for C1q; 95.1% for C2), and the equivalency of serum and plasma matrices was demonstrated. In patients with C3G and aHUS, C2 and C4 concentrations (and to a lesser extent C1q) were within reference limits, whereas CH50 activity and C3 concentrations were reduced. In inherited complement deficiency cohorts, C2 levels reflected the clinical diagnosis, including identification of a homozygous C2-null patient, while C1q measurements provided additional diagnostic insights. Normal CH50 activity was observed only when both C1q and C2 levels were normal or borderline.
Conclusion:
These new C1q and C2 immunoassays are analytically robust and provide a more complete complement profile when used alongside functional and other quantitative antigen testing.
