Venous thrombosis should be seen as a spectrum from calf deep venous thrombosis to pulmonary thrombo-embolism. All patients should be seen as high risk.


Differential diagnosis include:

»      cellulitis,

»     superficial thrombophlebitis,

»     chronic venous insufficiency,

»     lymphoedema,

»      popliteal (Baker’s) cyst,

»     internal derangement of the knee, and

»     calf muscle pull or tear


Diagnosis is primarily clinical and confirmed with imaging studies, e.g. Doppler.



Acute management

In pulmonary embolism, cardiovascular resuscitation may be necessary and surgery may be undertaken for intractable disease.


Superficial thrombosis does not require anticoagulation.

Distal venous thrombosis in the lower limbs, i.e. involving tibial veins only, need not be treated with anticoagulants. Monitor patients with repeat ultrasound if anticoagulants are not used. Ultrasonography should be repeated after a week but may be omitted if D-dimer is negative.


Advice on prophylaxis should be emphasised.

Eliminate all predisposing factors.


Prevent deep vein thrombosis.


Acute treatment

Unfractionated heparin initially, plus simultaneous warfarin. After 4–6 days, heparin is usually stopped and oral warfarin continued when a therapeutic INR level is reached.


Heparin and warfarin therapy should overlap for at least 5 days.

For proximal venous thrombosis and/or pulmonary embolism:

  • Unfractionated heparin, SC, 333 units/kg as an initial dose.
    • Follow 12 hours later by 250 units/kg/dose 12 hourly.
Units of unfractionated heparin Volume of heparin in mL (25 000 units/mL)
Weight (kg) Loading dose


12 hourly dose (units) Loading dose


12 hourly dose


35 kg 11 000 units 8 750 units 0.44 mL 0.35 mL
40 kg 13 000 units 10 000 units 0.52 mL 0.4 mL
45 kg 15 000 units 11 250 units 0.6 mL 0.45 mL
50 kg 17 000 units 12 500 units 0.67 mL 0.5 mL
55 kg 18 000 units 13 750 units 0.73 mL 0.55 mL
60 kg 20 000 units 15 000 units 0.8 mL 0.6 mL
65 kg 22 000 units 16 250 units 0.87 mL 0.65 mL
70 kg 23 000 units 17 500 units 0.93 mL 0.7 mL
75 kg 25 000 units 18 750 units 1 mL 0.75 mL
80 kg 27 000 units 20 000 units 1.07 mL 0.8 mL
85 kg 28 000 units 21 250 units 1.13 mL 0.85 mL
90 kg 30 000 units 22 500 units 1.2 mL 0.9 mL

Evidence indicates that PTT monitoring is not necessary with weight based dosing. However in morbid obesity and renal failure (eGFR < 30

mL/minute) unfractionated heparin should be used with PTT monitoring to maintain the PTT at 1.5 to 2.5 times the control.

PTT should be taken 4 hours after SC dose.


  • Low molecular weight heparin, e.g. enoxaparin, SC, 1 mg/kg 12 hourly.

Do not use LMWH in morbid obesity and renal failure (eGFR <30 mL/minute).

Thrombolytic therapy is indicated only in patients with angiographically confirmed early pulmonary embolism where haemodynamic stability cannot be achieved. Discuss with a specialist.


Prophylaxis is indicated for most medical and surgical patients.

Low molecular weight heparin, e.g.:

  • Dalteparin, SC, 5 000 units daily. OR
  • Unfractionated heparin, SC, 5 000 units 12 hourly.

Although the risk of bleeding is small, in the following patients prophylaxis should only be used under exceptional circumstances:

»      active bleeding,

»     intraocular, intracranial or spinal surgery,

»     lumbar puncture or epidural anaesthesia within 12 hours,

»      renal insufficiency,

»      coagulopathy, or

»      uncontrolled hypertension.

Heparin induced thrombocytopenia 

A severe immune-mediated drug reaction occurring in 1–5% of patients receiving heparin (unfractionated or low molecular weight heparin) therapy. It presents with thrombocytopenia and thrombosis. Diagnosis needs a high index of suspicion and should be considered if a patient has a 50% drop in platelet count within 5–10 days after initiating heparin therapy. Confirmation is done by positive antibody testing.

Stop heparin and refer all patients.


»              Heparin-induced thrombocytopenia.


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