This is a retrospective study to determine the accuracy and safety of a negative CT pulmonary angiogram (
CTPA) based on clinical outcome and to determine the usefulness of a negative
D-dimer assay before
CTPA. A total of 483 patients with a negative
CTPA study were followed up for 3 months, with the aim of detecting episodes of
venous thromboembolism and mortality. Three hundred and forty-nine patients had an immunochromatographic
D-dimer assay called 'Simplify', carried out before a
CTPA examination. Seventy-eight patients had a negative
D-dimer assay and a negative
CTPA. Three patients had a negative
D-dimer assay and a positive
CTPA. All three patients had a moderate pretest clinical probability. Of the 483 patients who had a negative
CTPA and a 3-month follow up, 444 (92%) were alive and 39 (8%) had died. Of the 444 patients who were alive, none had any further suspected episode of
thromboembolism or had received anticoagulation
therapy within the follow-up period. Of those who died, none of the deaths was thought to be as a result of
pulmonary embolism (PE). Single-detector helical CT can be used safely as the primary diagnostic test to evaluate PE. Negative Simplify
D-dimer assay and low pretest clinical probability exclude
CTPA-detectable PE, and a
CTPA is unnecessary in this cohort of patients.