Table 3

 Estimation of the (pre-test) clinical likelihood of pulmonary embolism

aPTT, activated partial thromboplastin time; INR, international normalised ratio.
High (>70% likely)Otherwise unexplained sudden onset of dyspnoea, tachypnoea, or chest pain and at least two of the following:
Significant risk factor present (immobility, leg fracture, major surgery)
Fainting with new signs of right ventricular overload on electrocardiography
Signs of possible leg DVT (unilateral pain, tenderness, erythema, warmth, or swelling)
Radiographic signs of infarction, plump hilum, or oligaemia
Intermediate (15%–70% likely)Neither high nor low clinical likelihood
Low (<15% likely)Absence of sudden onset of dyspnoea and tachypnoea and chest pain
Dyspnoea, tachypnoea, or chest pain present but explainable by another condition
Risk factors absent
Radiographic abnormality explainable by another condition
Adequate anticoagulation (INR>2 or aPTT >1.5 times control) during the previous week