Direct Thrombin Inhibitor Monitoring

Coagulation

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Description

Direct thrombin inhibitors (DTI’s) such as Argatroban and Dabigatran, are anticoagulants that exert their anticoagulant effect by directly binding to the active site of thrombin. Plasma concentrations of DTI’s can be monitored using a thrombin inhibitor assay. The principle of the assay is based on the inhibition of a constant defined amount of thrombin. The plasma sample is diluted, then a constant amount of purified human thrombin is then added and clotting is initiated. The clotting time is proportional to the concentration of DTI in the plasma.

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Indications

Argatroban is an anticoagulant that is administered following the patient developing Heparin Induced Thrombocytopenia (HIT). It has been demonstrated that the monitoring of Argatroban through APTT ratio as suggested by the manufacturer is inadequate due to plateaux effect of the APTT. This method will quantify the amount of Argatroban present with citrate plasma. There is a known prolongation of prothrombin time whilst on Argatroban and specific monitoring may be necessary when commencing warfarin treatment or when a patient has a prolonged baseline APTT.

Dabigatran is used in the prevention of VTE after having hip or knee surgery and more commonly used in patients for treatment of Stroke prevention and Atrial Fibrillation. Although no routine anticoagulant monitoring is required for Dabigatran, in specific circumstances such as suspected overdose or emergency surgery it may be clinically helpful to assess the anticoagulant activity in a patient.

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Sample Type

Plasma (Citrate 2.7ml Blue) x 1 or frozen (-80C) citrated (0.109M) single spun platelet poor plasma, frozen in less than 6 hours from venepuncture.

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Reference Range

Not indicated. See report for expected peak Dabigatran levels.

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Turnaround Time

Within 2 weeks (or on demand)

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Testing Frequency

As required (usually batched). Please contact the laboratory for urgent requests.

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External Notes

The accuracy of all coagulation tests are greatly influenced by pre-analytical variables. It is essential that the sample quality is given the highest priorities. Samples which fail to meet quality criteria including age of sample, specimen fill (>90%), haemolysed, clotted or activated samples will be rejected and a repeat sample requested.

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Patient Preparation

Time of sampling in relation to last dose is important for the interpretation of the measured DTI plasma concentration.

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References

Guy et al. Limitation of activated partial thromboplastin time for the monitoring method of the direct thrombin inhibitor argatroban. International Journal of Laboratory Haematology 2015:37(6)834-843.
Measurement of the Pharmacodynamic Effect of Dabigatran: Thrombin Clotting Time. J. Stangier, K. Wetzel, W. Wienen, K. Rathgen, J. van Ryn, Boehringer Ingelheim Pharma GmbH & Co KG, Biberach, Germany, P615 -Boston ISTH 2009. Dabigatran etexilate - a novel, reversible, oral direct thrombin inhibitor: interpretation of coagulation assays and reversal of anticoagulant activity. van RynJ., Stangier J., Haertter S.; Liesenfeld K.H., Wienen W., Feuring M, Clemens A., Thromb Haemost 2010; 103: 1116-112

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.