Diagnosis of pulmonary embolism

The diagnosis of pulmonary embolism is difficult. Positive results from ventilation-perfusion scanning or pulmonary arteriography confirm the diagnosis whilst a normal D-dimer makes the diagnosis of a pulmonary embolism very unlikely.

If a diagnosis of pulmonary embolism is suspected on the basis of history and clinical examination then urgent, and immediate, referral for secondary care review is indicated.

If pulmonary embolism (PE) is suspected and with a likely two-level PE Wells score then undertake either:

• an immediate computed tomography pulmonary angiogram (CTPA) or
  
  
• immediate interim parenteral anticoagulant therapy followed by a CTPA, if a CTPA cannot be carried out immediately.

If the CTPA is negative and DVT is suspected then consider a proximal leg vein ultrasound scan

If PE is suspected and with an unlikely two-level PE Wells score, then off a D-dimer test and if the result is positive offer either:

• an immediate CTPA or
• immediate interim parenteral anticoagulant therapy followed by a CTPA, if a CTPA cannot be carried out immediately

Notes:

• if patient has an allergy to contrast media, or who have renal impairment, or whose risk from irradiation is high:
  • assess the suitability of a ventilation/perfusion single photon emission computed tomography (V/Q SPECT) scan or, if a V/Q SPECT scan is not available, a V/Q planar scan, as an alternative to CTPA
  • if offering a V/Q SPECT or planar scan that will not be available immediately, offer immediate interim parenteral anticoagulant therapy
• a randomised controlled study evaluated the requirement for additional investigation if there was a negative D-dimer and a low clinical probability of pulmonary embolism (2)
  • in the low-probability group, venous thromboembolism (VTE) occurred during follow-up in 0 of 182 patients who had no additional diagnostic testing and in 1 of 185 patients who had additional testing (difference, -0.5 percentage point [95% CI, -3.0 to 1.6 percentage points])
  • in the moderate- or high-probability group, VTE occurred during follow-up in 1 of 41 patients who had no additional diagnostic testing and in 0 of 41 patients who had additional testing (difference, 2.4 percentage points [CI, -6.4 to 12.6 percentage points])
  • the authors concluded that, in patients with a low probability of PE who have negative D-dimer results, additional diagnostic testing can be withheld without increasing the frequency of VTE during follow-up. Low clinical probability and negative D-dimer results occur in 50% of outpatients and in 20% of inpatients with suspected PE

Reference:

• NICE (June 2012). Venous thromboembolic diseases: the management of venous thromboembolic diseases and the role of thrombophilia testing
• Kearn C et al. An evaluation of D-dimer in the diagnosis of pulmonary embolism: a randomized trial. Ann Intern Med. 2006 Jun 6;144(11):812-21.