A Clinical Approach for Defining the Threshold between Low and Medium Anti-Cardiolipin Antibody Levels for QUANTA Flash Assays

Abstract

Abstract:The threshold between low and medium antibody levels for anticardiolipin (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI) for the diagnosis of antiphospholipid syndrome (APS) remains a matter of discussion. Our goal was to create a protocol for determining the low/medium antibody cut-off for aCL antibody methods based on a clinical approach, and utilize it to establish the clinically-relevant low/medium threshold for QUANTA Flash aCL chemiluminescent immunoassay (CIA) results. The study included 288 samples from patients with primary APS (n = 70), secondary APS (n = 42), suspected APS (n = 36), systemic lupus erythematosus (SLE) without APS (n = 96) and other connective tissue diseases (n = 44). All samples were tested for IgG and IgM aCL antibodies with QUANTA Flash CIA, along with traditional enzyme-linked immunosorbent assays (ELISAs) (QUANTA Lite). The assay specific low/medium threshold for QUANTA Flash aCL IgG and IgM assays (i.e., the equivalent of 40 GPL and MPL units) was established as 95 and 31 chemiluminescent units (CU), respectively, based on clinical performance and comparison to QUANTA Lite ELISAs. Agreement between CIA and ELISA assay results improved substantially when the platform-specific low/medium antibody threshold was used, as compared to agreement obtained on results generated with the assay cutoff: Cohen's kappa increased from 0.85 to 0.91 for IgG aCL, and from 0.59 to 0.75 for IgM aCL results. This study describes a clinical approach for establishing the low/medium antibody threshold for aPL antibody assays, and successfully employs it to define 95 and 31 CU, respectively, as the low/medium cut point for QUANTA Flash aCL IgG and IgM results. This study can serve as a model for labs wishing to establish the appropriate low/medium aPL antibody threshold when implementing new aPL antibody assays.

Anti-Phospholipid Antibodies in COVID-19 Are Different From Those Detectable in the Anti-Phospholipid Syndrome

“…We found IgG/IgM aCL in 5.7/6.6% of patients, whereas anti-β 2 GPI IgG/IgA/IgM were found in 15.6/6.6/9.0% of patients. Similar values were obtained for aCL antibodies using CIA ( Table 2 ), whereas a slightly lower sensitivity was obtained for anti-β 2 GPI antibodies ( 26 ). The positivity for aCL and anti-β 2 GPI antibodies was at medium/low titer in contrast with the medium/high titers found in the control group of primary APS ( Figure 1 ).…”

Anti-phospholipid antibodies in COVID-19 are different from those detectable in the anti-phospholipid syndrome

“…We found IgG/IgM aCL in 5.7/6.6% of patients, whereas anti-β 2 GPI IgG/IgA/IgM were found in 15.6/6.6/9.0% of patients. Similar values were obtained for aCL antibodies using CIA (Table 1), whereas a slightly lower sensitivity was obtained for anti-β 2 GPI antibodies [25]. The positivity for aCL and anti-β 2 GPI antibodies was at medium/low titer in contrast with the medium/high titers found in the control group of primary APS (Figure 1).…”

Semiquantitative interpretation of anticardiolipin and antiβ2glycoprotein I antibodies measured with various analytical platforms: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

“…14,20 Others demonstrated that aCL IgG titers >40 GPL correlated more with APS-related clinical events and characteristics compared to positive aCL IgG titers <40 GPL, measured with ELISA. [21][22][23] Automated platforms using different techniques, such as CLIA and MFI, have some advantages over ELISA, are commercially available as alternatives for ELISA, and perform well. 24 However, they also show inter-assay variability and limited numerical agreement with ELISA.…”