Which diagnostic tests are recommended for confirming DVT in primary care settings?

For confirming deep vein thrombosis (DVT) in primary care settings, the diagnostic approach is guided by the clinical probability estimated using the 2-level DVT Wells score ¹,².

Initial Assessment:

• First, assess the person's general medical history and conduct a physical examination to exclude other causes of symptoms ¹.
• Then, use the 2-level DVT Wells score to estimate the clinical probability of DVT ¹,². This score categorises DVT as either 'likely' (2 points or more) or 'unlikely' (1 point or less) ¹,².

Diagnostic Tests Based on Wells Score:

• If DVT is 'likely' (Wells score 2 points or more):
  • Offer a proximal leg vein ultrasound scan, with the result ideally available within 4 hours ¹,².
  • If the ultrasound scan cannot be obtained within 4 hours, offer a D-dimer test, followed by interim therapeutic anticoagulation, and then a proximal leg vein ultrasound scan with the result available within 24 hours ¹,².
  • If the proximal leg vein ultrasound scan is positive, anticoagulation treatment should be offered or continued ¹. If the scan is negative, a D-dimer test should be offered ¹. If this D-dimer is positive, a repeat proximal leg vein ultrasound scan should be offered 6 to 8 days later ¹.
• If DVT is 'unlikely' (Wells score 1 point or less):
  • Offer a D-dimer test, with the result available within 4 hours ¹,².
  • If the D-dimer test result cannot be obtained within 4 hours, offer interim therapeutic anticoagulation while awaiting the result ¹,².
  • If the D-dimer test result is negative, interim therapeutic anticoagulation should be stopped, and alternative diagnoses considered ¹,².
  • If the D-dimer test result is positive, offer a proximal leg vein ultrasound scan, with the result ideally available within 4 hours ¹,². If the scan cannot be obtained within 4 hours, offer interim therapeutic anticoagulation and a proximal leg vein ultrasound scan with the result available within 24 hours ¹,².
  • If the proximal leg vein ultrasound scan is positive, anticoagulation treatment should be offered or continued ¹. If the scan is negative, and the D-dimer was positive, a repeat proximal leg vein ultrasound scan should be offered 6 to 8 days later ¹.

Important Considerations for D-dimer Testing:

• A negative D-dimer test, especially with an unlikely pre-test probability, can help exclude DVT ². However, a positive D-dimer result alone is not diagnostic and necessitates further testing ².
• D-dimer testing should be performed before starting interim therapeutic anticoagulation, as anticoagulation can affect the test result ².
• A point-of-care fully quantitative D-dimer test can be considered if laboratory facilities are not immediately available ¹. An age-adjusted D-dimer test threshold may be considered for people over 50 ¹.

For Pregnant or Postpartum Women:

• Immediate referral for same-day assessment and management is required ².
• D-dimer testing is not recommended for investigating acute VTE in pregnancy ². Low molecular weight heparin (LMWH) should be administered until the diagnosis is objectively excluded, unless strongly contraindicated ².