NB VTE in cancer patients:
Serious consideration should be given to the use of Low Molecular Weight Heparin in patients with cancer who experience a venous thrombotic event for 6 months, initially. There is evidence that Warfarin is inferior to LMWH in treatment of VTE in patients with cancer. Some consideration for use of DOAC in those who are needle phobic.
The following are not indications for anticoagulation
Ischaemic stroke: No evidence to support use of oral anticoagulants in completed stroke
unless patient has atrial fibrillation or a potential cardiac source of embolism (see ‘contraindications’ below). Consider aspirin or Clopidogrel as secondary prophylaxis.
Atrial fibrillation: Low risk patients (CHADS2 VASC <1, under 65, no diabetes, no stroke or TIA, no hypertension or other antiplatelet agent e.g clopidogrel, normal LV function) Treat with aspirin alone.
Peripheral arterial thrombosis and grafts: Consider aspirin or clopidogrel as secondary prophylaxis.
Coronary artery thrombosis:
Consider aspirin or Clopidogrel as secondary prophylaxis (75 mg daily for both). Insufficient evidence to justify full oral anticoagulation unless mural thrombus detected
Coronary artery graft thrombosis: Consider aspirin and/or clopidogrel as secondary prophylaxis. Incidence of vein graft occlusion in first month is 10-20% – this is reduced by aspirin but not warfarin.
Coronary angioplasty and coronary stents: Consider aspirin and clopidogrel as first-line therapy for drug-eluting stents.
Raised INR guidance: Reference 1. British Journal of Haematology 1998, 101 374-387. Reference2. British Journal of Haematology 2000, 109 704-715.
Anticoagulation with DOACS
There are five direct-acting oral anticoagulants, recently licenced and NICE approved. One of these, Dabigatran, is an anti-thrombin. The other four (Rivaroxaban, Apixaban, Edoxaban and Betrixaban) are anti-Xa drugs.
They have variable renal clearance (ranging from 70% for Dabigatran to 25% for Apixaban). For that reason, it is imperative that renal function is measured before starting the drugs and at varying times during their use. Dabigatran should not be used with EGFR < 30ml/min or <15 ml/min for the anti – Xa drugs.
Because of their more predictable pharmacokinetics, generally the DOACs do not require monitoring. However, in some clinical situations e.g requiring urgent surgery or at extremes of weight, they may. The dilute thrombin time measures Dabigatran and anti- Xalevels (using specific standards) measures the anti- Xa drugs.
Anticoagulation during pregnancy
Women who become pregnant whilst on warfarin will need to be transferred to low molecular weight heparin (LMWH) immediately – as warfarin is teratrogenic in 4% of pregnancies during 1st trimester (6-12 weeks). Similarly, if using a DOAC, this should be discontinued and switched to LMWH.
In general, initial anticoagulation is using LMWH (either for prophylaxis, or weight adjusted dose for treatment, recently changed to once daily) depending on indication, by subcutaneous injection. Patients are supervised by the Maternity Day Assessment Ward and anti- Xa levels are checked approximately monthly to ensure therapeutic compliance.
This service can be initiated through Dr. Yin Thi or Dr Thomas – Tel Ext: 32729; 33117 or by bleep through hospital switchboard.
Investigation of patients with possible venous thromboembolism
If there is clinical suspicion of a DVT or PE then a D-Dimer sample should be sent to the laboratory according to DVT management pathway. D-Dimer is an extremely sensitive test with a negative predictive value for DVT/PE in excess of 96%, (<0.5 being the cut off value). This should be used together with a clinical prediction score e.g. ‘Wells’. If low Wells score and negative D-Dimer, the patient can be discharged. Remember to check clotting screen, platelet count, urea & electrolytes, and LFT at baseline before commencing any anticoagulants. Use of the nurse-led DVT pathway (ext 31978) should be encouraged for probable DVT.
Investigation of patients for thrombophilia
Generally, inherited thrombophilia does not increase the risk for recurrent venous thrombosis, therefore should not be requested following an event unless there is a strong family history in those less than 40 years . Also, thrombophilia testing should not be requested following an acute VTE event as it will be difficult to interpret the results. Also, the result will not influence the intensity or duration of anticoagulation. Inherited thrombophilia does not influence the risk of arterial thrombosis. In young patients (age <50 years) samples for Lupus anticoagulation or Anticardiolipin antibodies may be considered.
Thrombophilia samples should not be taken when patients are on anticoagulation, oral contraception, HRT or when pregnant, for similar reasons.
Inherited thrombophilia in absence of thrombosis: give prophylaxis in high risk situations. Prophylaxis should be considered in pregnancy even in the absence of previous thrombosis because of high risk situations such as 1st degree family members.
Decisions regarding the need to perform thrombophilia testing should always be vetted by a senior Haematologist – preferably Dr Thomas.
Coagulation problems can be discussed with Dr Thomas, or the on-call Consultant Haematologist – available on bleep via Derriford Hospital Switchboard
Guidelines for anticoagulation control by point of care testing
INR monitoring is an integral part of care for the VKA anticoagulated patient with vitamin K antagonists (e.g. warfarin) and must be performed according to set criteria. Historically, this has involved taking intravenous (IV) blood samples and performing an INR using hospital-based Coagulation machines. Locally, the GP’s manage oral anticoagulation control according to shared-care guidelines originating from Derriford Hospital. Inevitably, there will be difficulties in obtaining IV samples in some, along with geographic, work and social reasons together with increasing paediatric numbers. Clearly, POCT for control of Warfarin will become more necessary.
The Royal College of Pathology (RCPath) guidance in this respect stipulates that laboratories should take the lead regarding all POCT hence the need for this guideline.