# Investigation of the Suitability of the ROTEM Assay to Measure Coagulation Potential in Blood From Patients on Concizumab Prophylaxis

## TL;DR

This study evaluates whether a modified ROTEM assay can reliably monitor coagulation in patients using concizumab for hemophilia, but finds it unsuitable due to inconsistent results.

## Contribution

The study introduces a modified ROTEM assay to assess coagulation in patients on concizumab and evaluates its suitability for clinical monitoring.

## Key findings

- In vitro experiments showed concizumab reduced clot time and increased clot development in hemophilia-like blood.
- ROTEM parameters weakly correlated with concizumab exposure and thrombin generation, indicating limited clinical utility.
- The modified ROTEM assay showed inconsistent performance and cannot be recommended for general monitoring.

## Abstract

Rotational thromboelastometry (ROTEM) aims to measure the coagulation potential in whole blood. Concizumab, an anti‐tissue factor pathway inhibitor (TFPI) antibody for prophylaxis in haemophilia, enhances tissue factor (TF)‐initiated coagulation by preventing inhibition of activated factor X (FXa), thus increasing thrombin generation.

To evaluate a modified ROTEM assay for monitoring patients on concizumab prophylaxis.

The TF reagent (r_exTEM) was diluted 50,000‐fold to make the ROTEM assay sensitive to haemophilia and to concizumab. The effect of concizumab was evaluated in the modified ROTEM in haemophilia A (HA)‐like blood (normal blood with added anti‐FVIII antibody). ROTEM analysis was performed in blood from patients participating in the explorer7/8 trials during 24 weeks of concizumab prophylaxis. Rotrol N plasma was used as quality control.

In vitro experiments showed concizumab concentration‐dependent reduction in clot time (CT) and increase in clot development (α‐angle) in HA‐like blood. At three of four clinical sites, CT and clot development were stable, variance of the control plasma was ≤12.4% and TF content of the diluted reagent (r_exTEM) was consistent. At these three sites, the correlation between CT versus concizumab exposure, free TFPI and thrombin generation assay parameters was weak (‐0.508 to +0.359). Prothrombin time positively correlated with CT (0.523) and negatively correlated with α‐angle (‐0.659).

Due to the poor correlation between ROTEM parameters, concizumab exposure, free TFPI and thrombin generation parameters and the lack of consistent and reliable performance of the modified ROTEM assay, it cannot be recommended for general monitoring of patients on concizumab prophylaxis.