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Likelihood Ratio (LR) in Emergency Medicine


Can we fight against Pulmonary Embolism using the LR’s arrows?

Clinical Scenario

A 80 y/o woman presented to the ED for dyspnoea.
She underwent a knee replacement 2 weeks ago, RR is 24, O2 saturation is 88%. HR is 90, the knee is edematous.
You are going to hunt a pulmonary embolism (PE)
While you phone the radiologist for a thorax CT scan you have an idea:

Can a compression ultrasonography (CUS) helps to avoid a CT?


Using Wells Score in this setting the PE pretest probability is intermediate (around 30%). 
Effectively the post test probability after a positive CUS is very high. Diagnosing a deep vein thrombosys (DVT) in patients with suspected PE doesn’t require other tests: the treatment of DVT with or without associated PE is the same.  
On the other hand after a negative CUS you need to keep hunting…


Emergency Medicine Australasia (2005) 17, 322–329
Likelihood ratios increase diagnostic certainty in 
pulmonary embolism 
K Chu and A FT Brown

Journal of Internal Medicine 250: 262-264
Utility of ultrasound imaging of the lower extremities in the diagnostic approach in patients with suspected pulmonary embolism
PS Wells et al
to be continued...

Ciro Paolillo


  1. Hi Ciro. thank you for this new clinical scenario. I think the big issue in pulmonary embolism is a rule-out test when d-dimer is positive (it happens all the time). the SPES study (Accuracy of Multi-organ Ultrasound -Venous, Cardiac and Thoracic- for the Diagnosis of Pulmonary Embolism) is actually recruiting patients. I hope that a complete negative ultrasound algorhytm (negative CUS, normal heart and no pleural or subpleural lesions)could have a sufficient negative LR to exclude PE in moderate risk patients...Mauro

  2. Hey I just came through your blog. Its really nice way to define. You share some good information about Pulmonary Embolism.
    Pulmonary embolism is a blockage in an artery in the lung. It is usually due to a blood clot that has traveled to the lung from another part of the body, usually the leg.
    Blood Clot Symptoms