Conferences and Medical Updates




Saturday, November 14, 2015

8:27 AM


For example, in patients who have a low pretest probability of PE, the so-called PERC (Pulmonary Embolism Rule-Out Criteria) algorithm should be applied. Those patients who meet all eight PERC items should not undergo either imaging or plasma D-dimer tests.

Instead, the ACP now recommends clinicians should take the following steps, depending on a patient’s pretest probability of PE:

  • Obtain a high-sensitivity D-dimer measurement as the initial test only if the patient has an intermediate pretest probability of PE, or else a low pretest probability without meeting all of the PERC criteria. Avoid imaging as the initial test in patients with a low or intermediate probability of PE.
  • Since normal D-dimer levels increase with age, use age-adjusted D-dimer thresholds (age × 10 ng/mL rather than a generic 500 ng/mL) in patients older than 50 to determine whether imaging is appropriate.
  • Do not order imaging studies in patients with a low age-adjusted D-dimer level.
  • Do not order D-dimer testing for patients with a high pretest probability of PE; instead, order computed tomography pulmonary angiography (CTPA) while reserving ventilation-perfusion scans for situations in which CTPA is contraindicated or unavailable.





Modified Wells Scoring System

The AAFP/ACP guideline advocates use of the Modified Wells prediction rule for the above-specified estimation and interpretation requirements (see Table 1, below). However, the guideline notes that the Wells rule performs better in younger patients without comorbidities or a history of venous thromboembolism. Current evidence also suggests this tool is effective in pregnant patients.[8] 

Moreover, the objective components of the Wells (Canadian Pulmonary Embolism Score) criteria have been shown to have little effect on the stratification power of the criteria; virtually all of the classification power is associated with a physician’s subjective prejudgment of the likelihood of pulmonary embolism.

Table 1. Modified Wells Prediction Rule for Diagnosing Pulmonary Embolism: Clinical Evaluation Table for Predicting Pretest Probability of Pulmonary Embolism* (Open Table in a new window)

Clinical Characteristic Score
Previous pulmonary embolism or deep vein thrombosis + 1.5
Heart rate >100 beats per minute + 1.5
Recent surgery or immobilization (within the last 30 d) + 1.5
Clinical signs of deep vein thrombosis + 3
Alternative diagnosis less likely than pulmonary embolism + 3
Hemoptysis + 1
Cancer (treated within the last 6 mo) + 1
Clinical Probability of Pulmonary Embolism Score
Low 0-1
Intermediate 2-6
High ≥6
*Reprinted from Am J Med, Vol. 113, Chagnon I, Bounameaux H, Aujesky D, et al, Comparison of two clinical prediction rules and implicit assessment among patients with suspected pulmonary embolism, pp 269-75, Copyright 2002.


Next Section: Revised Geneva Scoring System