A deep vein thrombosis commonly presents with pain, erythema, tenderness, and swelling of the affected limb. Findings on examination include a palpable cord (reflecting a thrombosed vein), warmth, ipsilateral oedema, or superficial venous dilation. Differential diagnoses include a ruptured Baker's cyst, muscle tears or pulls, and infective cellulitis. Objective diagnosis of deep vein thrombosis (as with pulmonary embolism) is important for optimal management, and although the clinical diagnosis is imprecise, models based on clinical features are fairly practical and reliable in predicting the likelihood of an event. Only a minority of patients (less than a third) with suspected deep vein thrombosis of a lower limb actually have the disease.
Compression ultrasonography remains the non-invasive tool of choice for the investigation and diagnosis of clinically suspected deep vein thrombosis. Although such imaging is highly sensitive for detecting proximal deep vein thrombosis, it is less accurate for isolated deep vein thrombosis of the calf. The ideal method, invasive contrast venography, is used when a definitive answer is required.
Newer imaging techniques being developed (for example, magnetic resonance venography, computed tomography) could detect pelvic vein thromboses, although further testing is necessary to establish their role in the diagnosis of deep vein thrombosis. Blood tests such as for fibrin d-dimer, a fibrin degradation product, add to the diagnostic accuracy of the non-invasive tests. d-dimer levels are > 500 ng/ml in nearly all patients with venous thromboembolism. Alone, they are insufficient to establish the diagnosis as such levels are non-specific and often can be found in patients admitted to hospital and in those with malignancy or after recent surgery. Thus, a low or normal d-dimer level with a low pretest probability makes a diagnosis of deep vein thrombosis (or pulmonary embolism) unlikely. shows a practical approach to the diagnosis of deep vein thrombosis using the pretest probability model and a clinical approach to diagnosis.
Fig 1 Clinical approach to the diagnosis of deep vein thrombosis. Adapted from Ho et al1
Venous thromboembolism, comprising deep vein thrombosis and pulmonary embolism, are common and treatable in hospital and the community
Major risk factors include age, recent surgery (especially orthopaedic), cancer, and thrombophilia
Established treatments are unfractionated heparin, low molecular weight heparin, fondaparinux, and warfarin
Treatment agents and duration depend on the cause