Laboratory assay measurement of modified clotting factor concentrates: a review of the literature and recommendations for practice

Abstract

Summary Over the past several years, novel modified clotting factor concentrates (CFCs) have been introduced into practice and are now widely prescribed in the countries where they are licensed. These products allow for less frequent infusions of CFC, thereby providing improved convenience and/or higher trough levels. They have been extensively studied for prophylaxis, episodic treatment of bleeding and for surgical prophylaxis. One issue that has emerged regarding the clinical application of these products revolves around the measurement of infused CFC in the clinical coagulation laboratory. Recent studies have demonstrated significant problems with the measurement of correct FVIII/IX levels following infusion of novel CF VIII/IX concentrates. The source of this problem appears to be related to the tremendous variability of the APTT reagents that are used in the one‐stage clotting assay, the most commonly used assay for determining factor levels. More specifically, the issue is related to the type of activator used in the reagents. Depending on the combination of the CFC and the APTT activator, the observed results may be either under‐ or overestimated to degrees that would be clinically relevant. Recommendations based on a review of published information regarding the potential for incorrect measurements of factor VIII/IX levels following infusion of recently developed, novel factor VIII/IX CFCs are presented for the clinician to use in clinical practice.

FIX potency of rFIX‐Albumin fusion protein is underestimated by one‐stage methods using silica‐based APTT reagents

“…In summary, the vulnerability of OS methods for FIX activity determination of EHL‐rFIX´s, due to deviation from the ‘like‐vs‐like’ principle, is in sharp contrast to analysis of pdFIX sources . Rather than advising against use of CS methods and an OS method with SynthAFax by referring to the discrepancy vs OS methods using silica‐based APTT reagents, the results obtained in this study should encourage a careful review of the situation by concerned parties.…”

Activity measurements of dalcinonacog alfa

“…It is widely known that assay discrepancies exist when measuring the potency of both full-length and modified recombinant FIX products against plasma and plasma-derived Concentrate FIX standards using different methods and reagents. [4][5][6][7][8][9][12][13][14][18][19][20][21][22] In this study, the degree of assay discrepancies of a novel modified rFIX therapeutic, dalcinonacog alfa (DA), was investigated and compared to those observed when assaying a plasma-derived TA B L E 3 Overall geometric mean (GM) and method GM (one-stage clotting assays (OSCA) and chromogenic assays (ChA)) as well as inter-assay variability (% geometric coefficient of variation (GCV) or range where only 2 kits tested) for plasma-derived FIX (PD), recombinant FIX (RB) and dalcinonacog alfa (DA) against the plasma-derived concentrate international standard: S1 and the plasma international standard: S2 (PD) and full-length rFIX (RB). No assay discrepancies were observed with PD against either standard.…”

“…10,11 Nevertheless, statistically valid assays and their estimates can be obtained when these modified products are assayed against the IS, which justify potency labelling in International Units (IU). [3][4][5][6]8,[12][13][14] Catalyst Biosciences has developed a new rFIX therapeutic, dalcinonacog alfa (DA) (previously known as CB2679d/ISU304), which has been given orphan drug designation in Europe and the United States and has currently completed a Phase 1/2 proof of concept clinical trial. 15 DA is a full-length recombinant FIX molecule with amino acid substitutions in the protease domain that confer the product with increased potency, enhanced FVIIIa binding and reduced inhibition by antithrombin.…”

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

“…1 Accurate postadministration monitoring of FVIII activity is required to guide an appropriate dosing regimen during on-demand or prophylactic treatment. 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. 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.…”

“…3 The introduction of extended half-life recombinant FVIII (rFVIII) products has presented some challenges for clinical laboratories that use OSC assays to monitor the activity of unmodified FVIII products. 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. 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.…”