Background: Measurement of fibrinogen with the Clauss assay is a thrombin time-based method that can be affected by Direct Thrombin Inhibitors. Argatroban is a direct thrombin inhibitor used in patients being treated for HIT and VITT.

Aims: To highlight the relative sensitivities of Clauss thrombin assays to argatroban.

Methods: A supplementary exercise for argatroban and fondaparinux included samples containing argatroban from a pool of treated patients and from a spiked normal plasma. Participants were requested to return Fibrinogen assay results. In addition, a regular Laboratory Programme exercise (survey 249) included a sample for fibrinogen assay from a patient undergoing plasma exchange and receiving argatroban for VITT.

Results: Samples distributed as part of an argatroban exercise (A21:01-05) and as part of the laboratory programme (249 21:31) in 2021 are detailed in table 1.

Conclusion(s): Commercial reagents for Fibrinogen quantitation have a range of thrombin concentrations and it is clear that the level of argatroban in patient or spiked samples can interfere with the measurement of fibrinogen. The data from the samples distributed highlight the fibrinogen underestimation with some assays in samples with levels of argatroban at therapeutic levels. Manufacturer’s inserts do not describe any assay limitation with regard to argatroban or other direct thrombin inhibitor.

Table

Table 1

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/measurement-of-fibrinogen-using-two-concentrations-of-thrombin-with-patients-receiving-argatroban-or-normal-plasma-spiked-with-argatroban-a-review-of-uk-neqas-blood-coagulation-exercises-2021/