Approach
Thrombotic risk varies with the reason for admission to hospital and the characteristics of the patient. Physicians should evaluate the risk of VTE in all patients admitted to hospital, while also considering bleeding risk and any contraindications to pharmacological VTE prophylaxis. Baseline investigations include renal function and full blood count (FBC), with coagulation profile if coagulation disorder is suspected.
Risk stratification for venous thrombosis
General guidelines address options for prophylaxis according to the type of patient (medical or surgical) and the type of surgery. Thromboprophylaxis must then be tailored to the individual patient in terms of additional VTE risk factors.[52]
Key risk factors include previous VTE (deep vein thrombosis [DVT] and/or pulmonary embolism [PE]), thrombophilia, malignancy, postoperative setting, trauma, indwelling central catheter (upper or lower extremity), and immobility. Other risk factors include chronic medical conditions, admission to intensive care, neurological disease with extremity paresis, increasing age, obesity, oestrogen-containing contraceptive pills and hormone replacement therapy (HRT), androgen-deprivation therapy, varicose veins, pregnancy and up to 6 weeks postnatal, first-degree relative with a history of VTE, and extended travel. However, these often have conflicting evidence.
Risk stratification for bleeding (patient-related factors, spinal anaesthesia, neurosurgical procedures)
Because pharmacological anticoagulation agents are considered the mainstay of VTE prophylaxis, risk stratification for bleeding must be assessed. Pharmacological agents are contraindicated if the patient presents with active bleeding, severe thrombocytopenia, or a coagulation disorder.[3] Baseline FBC and coagulation parameters (if a coagulation disorder is suspected) help rule out these contraindications. Non-pharmacological agents, including graduated compression stockings (GCS) and intermittent pneumatic compression (IPC) devices, are recommended in patients at high risk of bleeding.[3] Clinical scores can help assess the risk of bleeding and guide clinical decisions. The IMPROVE bleeding risk score has been prospectively validated and can help make the decision whether to administer a pharmacological thromboprophylaxis.[53][54]
An assessment of bleeding risk must also consider the presence of neuraxial anaesthesia and analgesia. Spinal haematoma (symptomatic bleeding within the spinal neuraxis) is a rare, but potentially catastrophic complication of spinal or epidural anaesthesia, and the risk varies with factors such as age, associated abnormalities of the spine, underlying coagulopathy, and an indwelling neuraxial catheter during sustained anticoagulation.[55] Care must be taken to avoid giving anticoagulants close to catheter insertion and removal so that no clinically significant anticoagulant effect is present at the time of the procedure.
Baseline tests
Before initiating thromboprophylaxis, all patients should have the following tests performed.
Renal function: agents such as LMWH and fondaparinux are eliminated through the kidney and must be used with caution in patients with chronic kidney disease.[56][57] Before starting thromboprophylaxis, creatinine should be measured and creatinine clearance subsequently calculated.
FBC: this will rule out an acute drop in haemoglobin or severe thrombocytopenia, which are contraindications to pharmacological thromboprophylaxis.
Coagulation profile: this should be ordered if a coagulation disorder is suspected.
Serum anti-PF4 antibodies: this should be ordered if there is a clinical suspicion of HIT while the patient is receiving UFH or LMWH (>50% drop in platelet counts, arterial or venous thrombosis while the patient is receiving heparin).
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