Score to Pretest Probability:
- 0-1 = 3.4%
- 2-6 = 27.6%
- >6 = 78.4%
The generally accepted "miss rate" for PE is 2%, meaning Well's alone cannot "rule out" PE with acceptable sensitivity. One method for clinically excluding PE is to apply the PERC rule if Well's score is ≤ 2-4.
For patients with high pretest probability of PE (ex: higher Well's Scores), D dimer does not exclude the diagnosis even if negative.
A study in 2007 (see below) found that in patients with Well's Score ≤ 4 and a negative ELISA D dimer assay (Vidas), 0.4% had a PE (2 patients, in both cases further testing was not clearly indicated).
D dimer can be measured using quantitative latex agglutination test (sensitivity 85-90%), whole blood agglutination (sens. 85-90%), or ELISA (sens. >95%, spec. 40%).
Suggested algorithm for PE workup, by EM:RAP / Cameron Berg:
Wells PS et al. Derivation of a simple clinical model to categorize patients' probability of pulmonary embolism: increasing the model utility with the SimpliRED d dimer. Thromb Haemost. 2000; 83:418.
Goekoop, RJ et al. Simple and safe exclusion of pulmonary embolism in outpatients using quantitative D-dimer and Wells' simplified decision rule. Thromb Haemost. 2007; 97(1):146-50.
Orman, Rob and Berg, Cameron. Accelerated Diagnostic Pathway: PE. EM:RAP. May 2015. Link