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HAEMOSTASIS


bleeding, it would seem logical to continue treatment. Patients with VTE provoked by a transient risk factor or a thrombosis confined to the calf veins have a low risk of recurrence and continued anticoagulation is not generally recommended in this group. Evidence suggests that patients with an unprovoked VTE have a recurrence risk of about 9% in the first year after ceasing treatment. Given that this risk exceeds the risk of treatment-related bleeding, it is now recommended that this group of patients should be considered for long-term anticoagulation. This patient group is, however, heterogeneous and the decision about whether or not to continue with long-term anticoagulation should be made on an individual basis, taking into account the relative risk factors. Factors that are associated with a higher risk of recurrence include male gender, elevated D-dimer measured after stopping treatment, and post-thrombotic syndrome. The presence of an inherited thrombophilia is not predictive of recurrence. The presentation of the initial thrombosis may also influence the decision. If presentation was pulmonary embolism (PE) the chance of PE recurrence is three to four times greater than that of deep vein thrombosis, and the risk of fatal PE is two to four times more likely in patients with symptomatic PE compared to patients with symptomatic DVT alone. If oral anticoagulation is stopped following an unprovoked VTE it is recommended to test for antiphospholipid antibodies as their presence may favour the resumption of anticoagulation.


Managing over-anticoagulation Dr HenryWatson (Aberdeen) considered over-anticoagulation and bleeding in his presentation, BCSH Guidance on Managing Over-Anticoagulation. The management of over-anticoagulation with vitamin K antagonists depends on the degree of over-anticoagulation and the severity of any associated bleeding. Major (limb or life-threatening) bleeding necessitates urgent reversal of the anticoagulant effect. This is rapidly and best achieved by the administration of a clotting factor concentrate that contains factors II, VII, IX and X, together with intravenous vitamin K, as the infused clotting factors each have a finite half life. The use of fresh frozen plasma produces suboptimal reversal of the oral anticoagulant effect and its use is only recommended if clotting factor concentrates are not available. All hospitals managing warfarin should stock a licensed clotting factor concentrate product. Non-major bleeding can be managed by temporary discontinuation of anticoagulant and administration of


MARCH 2012


‘Warfarin is a common medication, prescribed to an estimated 500,000 individuals in the UK and generating around nine million NHS prescriptions last year.’


intravenous vitamin K. Intravenous, as opposed to oral, vitamin K is the preferred choice when patients are bleeding because the INR correction is more rapid. It is well established that statistically the incidence of bleeding increases almost exponentially with increasing INR above about 5.0. The individual bleeding risk is, however, more difficult to define and thus management options for such patients must take individual circumstances into account. It is recommended that if the INR is between 5.0 and 8.0 then treatment should be stopped for one or two days and then resumed at a lower dose unless there is a high individual risk of bleeding, in which case oral vitamin K should also be considered. If the INR is greater than 8.0, oral vitamin K is recommended. In all cases, the possible cause of a high INR should be sought.


Warfarin and medical negligence The morning session of the first day concluded the anticoagulation theme with a presentation by Dr Trevor Baglin (Cambridge) entitled Why the Lawyers Love Warfarin: Legal Cases.Warfarin is a common medication, prescribed to an estimated 500,000 individuals in the UK and generating around nine million NHS prescriptions last year. It is also a high-risk drug, its absorption, pharmacokinetics, pharmacodynamics and consequent dose response being significantly influenced by genetic and environmental factors. Frequent dose monitoring and adjustment according to the INR are therefore required to ensure the anticoagulant effect is maintained within a suitable window of acceptability for each individual. Management of patients taking warfarin is a specialised role and should only be undertaken by suitably trained staff with the appropriate expertise. Given the above, it is not surprising that warfarin is one of the most common drugs cited in medical negligence claims. Negligence claims are covered by civil law and based on the premise that individuals are entitled to an acceptable duty of care. Claimants need to demonstrate that they suffered a breech in


the duty of care they were owed, that they suffered harm and that it was the breech of the duty of care that caused the harm. Dr Baglin concluded by discussing the details of several specific cases in which negligence had been demonstrated. The importance of maintaining accurate and timely anticoagulant therapy-related patient records, including any relevant notes and comments, was emphasised. Practitioners involved in the management of patients taking oral anticoagulants are strongly advised to familiarise themselves with the British Committee for Standards in Haematology Guidelines on oral anticoagulation (4th edn), published in the British Journal of Haematology in 2011, and the National Patient Safety Agency Safety Alert 18 Actions that can make anticoagulation therapy safer, published in March 2007.


Platelet function disorders The afternoon session of the first day was chaired by Dr Steve Kitchen (Sheffield) and the first speaker was Dr Paul Harrison (Oxford) who presented on Platelet Function Disorders – Laboratory Diagnosis. Disorders of platelet function encompass a broad spectrum of abnormalities that may be inherited or acquired. While acquired abnormalities are relatively common and do not normally warrant complex investigation, inherited abnormalities are comparatively rare (some are very rare), can be associated with a significant bleeding diathesis and may require detailed specialist investigation. Many different tests and strategies are available to evaluate platelet function, ranging from relatively simple tests to evaluate platelet numbers and size, through more complex global screening tests, to very complex tests and assays to identify a specific defect. In the investigation of bleeding due to a suspected specific platelet defect, global screening tests such as the PFA- 100 produce rapid results and have a limited role. Results must, however, be interpreted with caution as they show varying sensitivity, particularly to some mild defects. The finding of a normal result does not necessarily exclude an abnormality and further investigation may be indicated. Specific tests are poorly standardised, technically challenging, time consuming and are affected by many pre- analytical variables. Consequently, they should only be undertaken by specialist laboratories with appropriate expertise. Tests include flow cytometry, light transmission aggregometry, whole-blood aggregometry, measurement of total and released adenine nucleotides, electron microscopy and molecular genetics. Specific tests of platelet function should only be performed following specialist


THE CLINICAL SERVICES JOURNAL 29


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