A field study evaluating the activity of N8‐GP in spiked plasma samples at clinical haemostasis laboratories

Abstract

Aim: N8-GP (turoctocog alfa pegol) is a glycoPEGylated, extended half-life human recombinant factor VIII (FVIII) shown to be an efficacious treatment for patients with haemophilia A. Accurate monitoring of replacement therapy helps ensure proper dosing, leading to better patient care. The objective of this field study was to evaluate the accuracy and intra-and inter-laboratory variabilities of N8-GP and rAHF (Advate ® ) FVIII activity (FVIII:C) measurements in clinical laboratories using their routine methods and reagents.Methods: Laboratories measured plasma samples spiked with 0.03, 0.2, 0.6 and 0.9 IU/mL N8-GP or rAHF. Samples were blinded, and laboratories were instructed to perform evaluations using their routine FVIII activity assays and calibrators. Results:Of the 67 participating laboratories from 25 countries, 60 used a one-stage assay, 36 used a chromogenic assay, and 29 used both one-stage and chromogenic assays. Participating laboratories used nine different activated partial thromboplastin time (aPTT) reagents, the most common being SynthASil ® and Actin ® FS. Most aPTT reagents recovered N8-GP close to target. Three silica-based aPTT reagents (APTT-SP, TriniCLOT™ and STA ® PTT-Automate) underestimated N8-GP, recovering 40%-83% of target concentration. For chromogenic assays, N8-GP and rAHF recoveries were comparable at all concentrations, with overall mean recoveries for both products close to 130%. Assay variability was similar for both assay types and both products; inter-laboratory variability was greater than intra-laboratory variability and highest at 0.03 IU/mL. Conclusions:Most clinical laboratories accurately measured N8-GP and rAHF when using their in-house one-stage or chromogenic FVIII:C assays. However, three silicabased aPTT reagents underestimated N8-GP recovery. K E Y W O R D S chromogenic assay, clinical laboratory techniques, factor VIII activity assay, haemophilia A, one-stage assay, postadministration monitoring S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Tiefenbacher S, Clausen WHO, Hansen M, Lützhøft R, Ezban M. A field study evaluating the activity of N8-GP in spiked plasma samples at clinical haemostasis laboratories. Haemophilia. 2019;25:893-901.

An overview of turoctocog alfa pegol (N8‐GP; ESPEROCT®) assay performance: Implications for postadministration monitoring

“…Target recoveries obtained using APTT-SP ranged between 30% and 50% across both sites. 11 The actual potencies of both N8-GP and ADVATE ® vials were used in the preparation of field study kits and were based on a chromogenic assay according to Figure 4A). 8 To further examine the accuracy of N8-GP activity measurements in the real world, a large field study was conducted during which clinical laboratories used their routine FVIII activity assays to test samples spiked with four different levels of N8-GP or unmodified rFVIII (ADVATE ® ) in the range of 0.03-0.9 IU/mL.…”

“…2 Although OSC assays have been traditionally used for clinical monitoring, emerging knowledge about their limitations has resulted in many laboratories adopting CS assays in recent years. 6,[8][9][10][11][12] Underestimation of FVIII activity is not desirable as it would add to treatment cost and potentially put patients at risk of thrombosis if the dosage is adjusted based on the result of the assay. 4,5 Substantial differences in inter-laboratory test results using some assays to monitor extended half-life molecules have been observed, a challenge that is compounded by the wide variety of reagents, instrumentation and methodology in use worldwide.…”

“…5 It is therefore important to identify assays that can be used to accurately monitor clinical postadministration samples and to communicate information regarding the most appropriate assays to use for monitoring to the clinical laboratories that perform these tests. [8][9][10][11][12] In this review, we give an overview of the programme undertaken by Novo Nordisk to characterize the functionality of N8-GP and examine the precision and accuracy of laboratory assays used to measure FVIII activity. [13][14][15] N8-GP can be administered every 4th day, reducing the burden of frequent prophylactic treatment.…”

“…2,6,7 Variations in assay results appear to be related to the type of contact activator used in the APTT reagent, with some silica-based APTT reagents underestimating the activity of extended half-life rFVIII molecules. 6,[8][9][10][11][12] Underestimation of FVIII activity is not desirable as it would add to treatment cost and potentially put patients at risk of thrombosis if the dosage is adjusted based on the result of the assay. 5 It is therefore important to identify assays that can be used to accurately monitor clinical postadministration samples and to communicate information regarding the most appropriate assays to use for monitoring to the clinical laboratories that perform these tests.…”

“…13 Some OSC assay reagents have been demonstrated to underestimate the activity of N8-GP. [8][9][10][11][12] In this review, we give an overview of the programme undertaken by Novo Nordisk to characterize the functionality of N8-GP and examine the precision and accuracy of laboratory assays used to measure FVIII activity. We review data collected during the non-clinical and clinical programmes and provide guidance for clinical laboratories to assist in the selection of appropriate reagents to measure N8-GP activity.…”