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Analysis Too Much Medicine

When a test is too good: how CT pulmonary angiograms find pulmonary emboli that do not need to be found

BMJ 2013; 347 doi: (Published 02 July 2013) Cite this as: BMJ 2013;347:f3368
  1. Renda Soylemez Wiener, assistant professor12,
  2. Lisa M Schwartz, professor34,
  3. Steven Woloshin, professor34
  1. 1Pulmonary Center, Boston University School of Medicine, Boston, MA, USA
  2. 2Center for Health Quality, Outcomes and Economic Research, ENRM VA Hospital, Bedford, MA, USA
  3. 3Dartmouth Institute for Health Policy and Clinical Practice, Dartmouth Medical School, Lebanon, NH, USA
  4. 4VA Outcomes Group, VA Medical Center, White River Junction, VT, USA
  1. Correspondence to: R S Wiener rwiener{at}
  • Accepted 14 April 2013

Summary box

  • Clinical context—Pulmonary embolism has been described as one of the most commonly missed deadly diagnoses

  • Diagnostic change—The introduction and rapid uptake of multidetector computed tomographic pulmonary angiography

  • Rationale for change—CT pulmonary angiography is much more sensitive than ventilation perfusion scanning so fewer pulmonary emboli will be missed

  • Leap of faith—Finding “missed” pulmonary emboli saves lives

  • Increase in disease—US data show 80% rise in incidence of pulmonary embolism between 1998 and 2006 after CT pulmonary angiography was introduced (from 62.1/100 000 to 112.3/100 000)

  • Evidence of overdiagnosis—Combination of large increase in incidence, reduced case fatality (in-hospital deaths among people with a diagnosis of pulmonary embolism), and a minimal decrease in mortality (deaths from pulmonary embolism in the population) suggests that many of the extra emboli being detected are not clinically important

  • Harms from overdiagnosis—Substantial increase in complications from anticoagulation. Anxiety and inconvenience for patients following diagnosis and treatment

  • Limitations—Evidence for overdiagnosis is derived from administrative data or single institution case series. Without prospectively observing untreated patients, it is impossible to be certain which emboli are not clinically important

  • Conclusion— CT pulmonary angiography has reduced missed pulmonary embolism but seems to result in overdiagnosis. We need to learn which small emboli need treatment

For decades clinicians have been taught that pulmonary embolism—defined by the National Institutes of Health as a “sudden blockage in a lung artery”1—always matters and to be vigilant because a missed embolism can be fatal.2 When a patient presents with shortness of breath, pleuritic chest pain, tachycardia, or signs of right heart strain, clinicians are trained to think “pulmonary embolism.” Because these symptoms and signs are neither sensitive nor specific, scoring systems (such as the Wells criteria) have been developed to help clinicians decide which patients to scan,3 although …

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