December 2012 – Evidence Based Emergency Medicine (Part One)
Posted on December 28, 2012
Every other month I spend two hours with the residents during their Wednesday lectures. Generally we review two journal articles using critical review forms (Critical Review Form – Diagnostic Test, Critical Review Form – Therapy) and group participation. Below is the summary of one of this month’s articles:
Safe exclusion of pulmonary embolism using the Wells rule and qualitative D-dimer testing in primary care: prospective cohort study. Geersing et al. BMJ 2012;345. (BMJ 2012 345 e6564)
SUMMARY: This study looked at using the Well’s criteria (http://en.wikipedia.org/wiki/Wells_score) along with a point of care, qualitative D-dimer to help safely rule out pulmonary emboli in an outpatient population presenting with worrisome signs. 598 adults with suspected PE were included in this study. A total of 12% of the patients had PEs. Patient with a Well’s score of less than or equal to 4 with a negative d-dimer could be safely excluded from having a PE (Negative Likelihood Ratio 0.02, meaning a patient with a 30% pre-test probability would have a < 1% risk of PE)
This study adds to the already large body of evidence that supports the use of clinical prediction rules (in low\moderate risk patients) combined with high quality d-dimer tests in excluding PE and reducing the need for imagining (including CTs).
Are the Results Valid?
Did the clinicians face diagnostic uncertainty? YES.
- Was there a blind comparison with an independent gold standard? Not entirely. Not all the patients received CT angio or other forms of imaging.
- Did the results of the test being evaluated influence the decision to perform the gold standard? Yes. A positive d dimer or elevated Well’s score would cause further testing to be done.
What are the Results?
- What likelihood ratios are associated with the range of possible test results?
- Using a Well’s score of < 5 and negative d-dimer:
- the Positive Likelihood Ratio was 1.52 (95% CI 1.25 – 1.55)
- The Negative Likelihood Ratio was .02 (95th% CI .01 – .34) (http://en.wikipedia.org/wiki/Likelihood_ratios_in_diagnostic_testing)
How can I apply the results to patient care?
- Will the reproducibility of the test result and its interpretation be satisfactory in my setting? Yes.
- Are the results applicable to my patients? The main limitation would be the fact that this study involved non-ED patients. However, it had a good prevalence and diagnostic uncertainty.
- Will the results change our management? Generally this study adds to the large body of evidence that supports the use of clinical prediction rules and high sensistivity d-dimers in ruling out PEs in low\moderate risk patients.
- Will patients be better off as a result of this test? Yes. This could significantly reduce radiation exposure and overtreatment in 10-30% of patients being evaluated for PE.