CHEST PAIN54 General Medical Emergencies
(i) A low pre-test probability on Wells’ criteria with a score of <2 has
up to 3.6% probability of PE.
(ii) A moderate pre-test probability with a Wells’ criteria score of 2–6
has a 20.5% probability of PE.
(iii) A high pre-test probability with a Wells’ criteria score of >6 has a
66.7% probability of PE.
10 Patients under 50 years old and with a low pre-test probability:
(i) Check if the PERC rule score is negative (see Table 2.4) and if
all criteria are fulfilled, no further testing is required and a PE is
ruled out.
Table 2.4 Pulmonary embolism rule-out criteria (PERC) rule in the low pre-test
probability patientAge <50 years
Pulse <100 beats/min
Pulse oximetry >94%
No unilateral leg swelling
No haemoptysis
No recent trauma or surgery
No prior pulmonary embolism or deep vein thrombosis
No oral hormone useIf all eight factors are fulfilled (negative), no further testing is required.
Modified from Kline JA, Mitchell AM, Kabrhel C et al. (2004) Clinical criteria to prevent
unnecessary diagnostic testing in ED patients with suspected pulmonary embolism.
Journal of Thrombosis and Haemostasis 2 : 1247–55.
11 Send a D-dimer test only in patients ≥50 years with a low pre-test probability,
or in any patient under 50 with a low pre-test probability but with one or
more PERC criteria positive (see Table 2.4).
(i) Check with the laboratory which D-dimer test they use and their
test’s reference ranges, in particular their normal cut-off range.
(ii) Discharge the patient if this D-dimer test is negative, i.e. there is
no PE.
(iii) Arrange imaging if the D-dimer test is positive (see below).
12 Perform a multislice, helical computed tomography pulmonary angiogram
(CTPA) if available, in all patients with a moderate or high pre-test probabil-
ity, and in those low pre-test probability patients with a positive D-dimer.
13 Alternatively, start with a ventilation–perfusion isotope lung scan, the V/Q scan.
(i) A V/Q scan is preferred when the patient is allergic to contrast
dye, has renal failure or is younger than 40 years, particularly in
females.