Deep vein thrombosis: patients with suspected DVT and a negative ultrasound scan were safely not treated while awaiting another scan.

Clinical bottom line (level 2b)

  1. In symptomatic patients with suspected deep vein thrombosis but a negative ultrasound scan, it was safe to withhold anticoagulants and repeat the ultrasound just once in a week.
  2. A negative result initial result did not exclude DVT
Cogo et al: British Medical Journal 1998; 316: 17-20
Expires May 2003

The study

Inception cohort study with objective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: thromboembolism services, Italy, Canada, Holland

1703 patients (aged range 18 to 96 yeras; mean 64, 61% female) clinically suspected first epidose of deep vein thrombosis

Excluded if
  • symptoms suggesting pulmonary embolism
  • past history of deep vein thrombosis
  • on anticoagulants >48 hours
  • venogram contraindicated
  • <18 years old
  • geographically inaccessible




    • 100% followed for 6 months
    Outcomes studied:
  • positive first USS
  • positive 2nd USS
  • thromboembolism- symptomatic while awaiting 2nd USS
  • thromboembolism- 1st USS negative but 2nd USS positive (no new symptoms)
  • thromboembolism- both USS negative, but symptomatic by 3 months
  • thromboembolism- both USS negative and no symptoms by 3 months

    • All patients had compression ultrasound of the common femoral and popliteal veins; this was repeated one week later. If first scan was negative, patients were not anticoagulated while awaiting the second.

    The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)    		 NNF
    (95% CI)
    positive first USS 6 months 400/1702 24%
    (21% to 26%)    		 4
    (4 to 5)
    positive 2nd USS 6 months 12/1702 0.71%
    (0.31% to 1.1%)    		 142
    (91 to 325)
    thromboembolism- symptomatic while awaiting 2nd USS 7 days 1/1703 0.06%
    (0.0% to 0.17%)    		 1700
    (-1770 to 575)
    thromboembolism- 1st USS negative but 2nd USS positive (no new symptoms) 7 days 12/1300 0.92%
    (0.40% to 1.44%)    		 109
    (70 to 250)
    thromboembolism- both USS negative, but symptomatic by 3 months 3 months 8/1290 0.62%
    (0.19% to 1.1%)    		 161
    (95 to 520)
    thromboembolism- both USS negative and no symptoms by 3 months 6 months 0/1272 0.00%
    (0.0% to 0.0%)

    Comments

    1. Compression ultrasound: (7.5 Mhx grey-scale real time)- femoral vein not traced, since it raises false positives.
    2. In effect this was a 'test' or 'validation' set.
    3. Protocol violated in 16/1290 (1.2%) with anticoagulation therapy or tests (one isolated calf DVT).
    4. Rule was not tested in patients with suspected PE

    Citation

    1. Cogo A, Lensing AWA, Koopman MMW, et al: Compression ultrasonography for diagnostic management of patients with clinically suspected deep vein thrombosis:prospective cohort study. British Medical Journal 1998; 316: 17-20
    Contributor: Dave Sackett, Chris Ball and Clare Wotton, May 2000
    Reviewer: Alex Gallus

    Clinical Question.
    Patient suspected DVT, low risk
    Intervention or Exposure witholding anticoagulation, serial ultrasound scans
    Outcome safety, mortality, morbidity, missed DVT