Deep vein thrombosis — prophylaxis and treatment

Risk factors (Virchow's triad). Stasis — immobility, hospitalisation, stroke with hemiplegia, long travel, heart failure. Endothelial injury — surgery, especially hip fracture and hip or knee arthroplasty, trauma, central venous catheters. Hypercoagulability — malignancy, sepsis, dehydration, previous VTE, oestrogens, nephrotic syndrome, thrombophilia. Advancing age is itself an independent risk factor, with incidence rising sharply after 70.

Clinical features and pitfalls. Unilateral calf or thigh pain, swelling, warmth, erythema, dilated superficial veins and calf tenderness; Homans' sign is unreliable. Clinical diagnosis alone is unreliable in the elderly. Differential diagnosis: cellulitis, ruptured Baker's cyst, dependent oedema, heart failure, lymphoedema, haematoma, superficial thrombophlebitis and post-thrombotic syndrome.

Diagnosis. Apply the Wells score to stratify probability. Low probability plus a negative D-dimer excludes DVT, but D-dimer specificity falls markedly with age, so use the age-adjusted cut-off (age × 10 µg/L for patients over 50) to avoid unnecessary imaging. Confirm with compression ultrasonography; if the initial scan is negative but clinical probability is high, repeat at one week or proceed to whole-leg scanning.

Prophylaxis. Early mobilisation and adequate hydration for all. Mechanical — intermittent pneumatic compression; note that graduated compression stockings are contraindicated after stroke (CLOTS-1 showed no benefit and more skin breaks). Pharmacological — LMWH (enoxaparin 40 mg subcutaneously daily; reduce to 20–30 mg if CrCl < 30 mL/min) or fondaparinux, for the duration of the acute illness; extended prophylaxis for 28–35 days after hip fracture surgery or hip arthroplasty. Always assess bleeding risk before prescribing.

Treatment. A DOAC is first-line — apixaban 10 mg twice daily for 7 days then 5 mg twice daily, or rivaroxaban 15 mg twice daily for 21 days then 20 mg daily; dabigatran and edoxaban require 5 days of parenteral LMWH lead-in. Use LMWH in severe renal impairment and in pregnancy, and warfarin (INR 2–3) for mechanical valves or antiphospholipid syndrome. Early ambulation with compression relieves symptoms; an IVC filter is used only when anticoagulation is absolutely contraindicated, and should be retrievable. Catheter-directed thrombolysis is reserved for limb-threatening iliofemoral thrombosis (phlegmasia).

Duration and complications. Provoked by a transient major risk factor → 3 months. Unprovoked, recurrent, or with a persistent risk factor such as active cancer → extended (indefinite) anticoagulation, using reduced-dose apixaban 2.5 mg twice daily or rivaroxaban 10 mg daily after the first 6 months. Complications: pulmonary embolism, post-thrombotic syndrome (up to 40%), recurrence and anticoagulant-related bleeding. After unprovoked DVT, perform age-appropriate cancer screening and a careful history and examination — extensive occult-malignancy imaging is not indicated.

API-CAT trial (NEJM 2025) — in patients with active cancer and proximal DVT or PE who had completed at least 6 months of anticoagulation, extended reduced-dose apixaban 2.5 mg twice daily for 12 months was non-inferior to full-dose 5 mg twice daily for recurrent VTE and caused significantly less clinically relevant bleeding (12.1% versus 15.6%). This supports dose de-escalation rather than discontinuation for extended treatment — particularly valuable in frail older patients with cancer-associated thrombosis.