Background: Risk minimization measures that need to be implemented to minimize the thrombotic risk associated with the use of combined oral contraceptives (COC) is controversial. Despite the regulatory bodies recommend the assessment of the ETP-based activated protein C (APC) resistance during the development of steroid contraceptives; results are not comparable between studies due to lack of validation and standardization. To overcome this issue, Qualiblood recently validated and standardized this assay but wide implementation of this validated assay needs further investigations.

Aims: To assess the inter-laboratory variability of the validated ETP-based APC resistance assay.

Methods: Analyses were performed on three different Calibrated Automated Thrombogram (CAT) with Thrombinoscope software (version 5.0 for CAT_1,2; version 2.0 for CAT₃) by three different operators to assess the inter-laboratory variability. The method targets a 90% of inhibition of the ETP in healthy donors. Therefore, dose-response curves (n=3) were performed to define the amount of APC depending on the equipment used and the operator (n=3). A homemade and a commercial reference plasma were used. Quality controls (n=3) and a subset of real-life samples (n=11) were tested on each equipment. All measurements were performed in duplicate.

Results: Dose-response curves did not show any significant differences between CAT₁ and CAT₂ (Dunn’s multiple comparison test; p-value>0.9999) (►Figure 1-2), whatever the dose-response curves were performed with the in-house or the reference plasma. When comparing samples between CAT₁ and CAT₂ at the defined concentration of APC, the mean deviation was 7.83%. As the software version of the CAT₃ was older, some modifications must be performed to ensure the transferability of the methodology. This is due to important background noise which limits the performance of this older version of the CAT₃ at low ETP-values.

Conclusions: These results demonstrate the transferability of the validated ETP-based APC resistance test between CATs using the same software version.

[FIGURE 1: Total variability between CAT1 and CAT2 (n=2 operators; n=3 dose-response curves/operator). ]

[FIGURE 2: Inhibition percentage at 6 levels concentration of APC with in-house reference plasma and commercial reference plasma on CAT1 and CAT2. ]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/inter-laboratory-variability-of-the-standardized-etp-based-apc-resistance-assay/