Although clinical findings are often inaccurate for diagnosing deep venous thrombosis (DVT), clinical prediction rules can be helpful (see accompanying table). Ofri reviewed the literature on the diagnosis and management of DVT.
The best diagnostic test available for DVT is venography, although magnetic resonance imaging may rival venography for accuracy. Doppler ultrasonography has a sensitivity and specificity of 95 percent for proximal DVT (popliteal and femoral veins are not fully compressible with the ultrasound probe in patients who have DVT). Ultrasonography is more accurate in detecting symptomatic, proximal and first-time DVTs than in detecting those that are asymptomatic, distal or recurrent. Impedance plethysmography is less sensitive than Doppler ultrasonography. The d-dimer assay has high sensitivity and negative predictive value but poor specificity, because a positive test (a high value) result can occur in patients with many other conditions including malignancy, disseminated intravascular coagulation and hepatic failure.
The best diagnostic approach depends on pretest probability as determined by clinical characteristics. In patients with a low pretest probability, a normal Doppler ultrasonogram is enough to rule out DVT. Abnormality on the ultrasonogram would require confirmation by venography. In patients with a high pretest probability of DVT, a positive finding on ultrasonography is sufficient to initiate treatment while a negative study result would require venography to rule out DVT. In a patient with moderate probability, a positive ultrasound result would support the initiation of treatment, but a negative test result might require repeat ultrasonography in one week. If the second test is normal, the patient can be reassured; if the test is positive, treatment is initiated. If the initial ultrasound result, as well as the d-dimer test result, is negative, the need for repeat ultrasonography is eliminated.
The reason for treating DVT is to prevent pulmonary embolism. Proximal DVTs are associated with a significantly higher incidence of pulmonary embolism if left untreated and must be treated early with heparin. Distal DVTs propagate less than 20 percent of the time and usually do so within one week. A patient with a distal DVT can be observed with serial ultrasonography, and treatment can be delayed until proximal propagation is noted. DVTs that remain confined to the calf are associated with a less than 1 percent risk of pulmonary embolism and a 2 percent chance of recurrent DVT.
Traditional treatment includes unfractionated heparin given until the dosage of sodium warfarin is therapeutic. The use of low-molecular-weight (LMW) heparin is becoming more common because it offers the advantages of having a more predictable anticoagulant effect, avoids the need for anticoagulation testing and allows the patient to be treated at home. It is also associated with less antibody formation, a lower risk of heparin-induced thrombocytopenia and a decreased overall mortality. Patients being treated at home must learn to give themselves subcutaneous injections and should have close follow-up. Warfarin therapy should be initiated on day 1 when using unfractionated or LMW heparin. After four to five days and when the International Normalized Ratio is greater than 2.0 for two consecutive days, the heparin therapy can be discontinued. In patients with idiopathic, first-episode DVT, anticoagulation therapy should continue for at least six months, although the optimal treatment time is unknown. Age and a history of prior thromboembolic events are strong risk factors for recurrence.
|Active cancer within six months||1|
|Paralysis, paresis or cast of lower extremity||1|
|Recently bedridden for more than three days or major surgery within the past four weeks||1|
|Localized tenderness along distribution of deep venous system||1|
|Calf diameter more than 3 cm larger than opposite leg†||1|
|Collateral superficial veins (nonvaricose)||1|
|Alternative diagnosis as likely or more likely than that of DVT||−2|
A work-up for thrombophilia is appropriate in patients younger than 50 years who develop DVT in the absence of any other risk factors, in patients with a family history of thromboembolic disease and in patients with a thrombosis of unusual location or severity. The work-up for genetic thrombophilias includes testing for deficiencies of protein S, C and antithrombin III, and the presence of antiphospholipid antibodies. Homozygosity for the factor V Leiden mutation confers a greater risk for thrombosis than heterozygosity. It is unclear if the presence of one of these thrombophilias in a patient with first-time DVT indicates a need for longer anticoagulation treatment, but the latter is probably appropriate in these patients.
Ofri concludes with the opinion that there is little utility in aggressive cancer work-up in patients after an initial episode of DVT. A thorough history, physical examination and age-appropriate cancer screening are adequate.
editor's note: The use of LMW heparin is becoming more common in the management of DVT. The specificity of its protein-binding characteristic makes the dose response more reliable and eliminates the need for anticoagulation monitoring in the vast majority of cases. The increasing use of LMW heparin preparations in a single daily dose has made this preparation available to more patients than twice-daily dosing regimens. Although unfractionated heparin and LMW heparin can cause decreased bone density, LMW heparin has less platelet inhibition; most studies show a lower incidence of heparin-induced thrombocytopenia when this preparation is used. Comparisons of other potential adverse effects are less clear. More health plans are encouraging the appropriate use of LMW heparin because of the decreased cost of care when hospitalization is avoided.—r.s.