Pulmonary embolism: helical CT can diagnose, but not safely exclude it in moderate risk patients

Clinical bottom line (level 1b)

40% of patient with a clinically suspected pulmonary embolism and an elevated d-dimer had one.
An abnormal helical CT scan could diagnose a PE (LR + 8.0) but not safely rule one out (LR - 0.33) .

Perrier et al: Ann Intern Med 2001; 135 : 88-97

Expires May 2004

The study

Setting: university hospital, Switzerland

299 patients (aged 21 to 99; median 69, 54% female) with a clinically suspected PE and d-dimer > 50 microg/l

Excluded if

expected to survive for < 3 months
contraindication to CT scan or scan unavailable
allergy to contrast agent
asthma
pregnancy
treated with oral anticoagulants at study entry or contraindication to oral anticoagulants
likely to be impossible to follow-up

Independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
Reference standard:

based on a validated algorithm including lower-limb compression ultrasonography, lung scanning and pulmonary angiography or follow-up for 3 months

Diagnostic test: helical CT scan: read by blinded radiologists 3 months after acquisition. Clot diagnosed if contrast media outlined a central intraluminal defect or if a vessle was totally occluded by low attenuation material.

The evidence

pre-test probability of pulmonary embolism: 40%, (95% CI: 35% to 46%)

diagnostic test	PE	no PE	LR+ (95% CI)	post-test probability	LR- (95% CI)	post-test probability
abnormal helical CT scan	81	15	8.0 (4.8 to 13)	84%	0.33 (0.25 to 0.44)	18%
total	116	171

K _{interobserver}0.82 - 0.90

Citation

Perrier A, Howarth N, Didier D, et al: performance of helical computed tomography in unselected outpatients with suspected pulmonary embolism. Ann Intern Med 2001; 135 : 88-97

Search Terms: from ACP Journal Club
Contributor: Chris Ball, May 2002
Reviewer:

_{Clinical Question.}

_Patient	_{suspected PE and positive d-dimer}
_{Intervention or Exposure}	_{helical CT scan}
_Outcome	_{pulmonary embolism}