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Likelihood Ratio (LR) in Emergency Medicine


Diagnosis of pneumonia. Is it the time for a combined imaging strategy?

A 80 yo man is brought from an assisted-living facility because of fever, productive cough, tachycardia and dyspnoea. 
He has a history of dementia and hypertension.
He is cachectic, you hear ronchi on the left side. 

How should you approach this patient?

In the Emergency department setting the pretest probability of pneumonia is 15%

It’s far in time when Laennec said that with the stethoscope doctors would have made a definitive diagnosis of pneumonia in every patient  (1819). 
In this case the presence of 4/5 clinical findings increases the probability of 40%, it is not bad, but it depends on pretest probability.
Any combination of clinical findings is not usefull to rule in or out the diagnosis of pneumonia, to confirm this you need a chest radiography….

but what if it is negative? 

Post test probability after negative supine X Ray 

A negative supine Chest X-Ray reduces the probability of pneumonia a little: about a 20%.  
Is it the time for a combined imaging strategy?



The supine position X-Ray, with a single anteroposterior view has a poor performance. If you are an ECO-expert try to perform an ultrasound at the bedside. Maybe you'll find a focused interstitial syndrome, or subpleural consolidation. If negative you can feel comfortable. Practice make perfect!!!
When the CT? when the diagnosis is unclear, or when you suspect any complication.   


Clinical prediction rule for pulmonary infiltrates.
Ann Intern Med 1990; 113 (9):664-670.
PS Heckerling et al. 

Does this patient have community-acquired pneumonia? Diagnosing pneumonia by history and physical examination.  
JAMA.  1997;278:1440–5.
JP Methlay et al. 

Lung ultrasound is an accurate diagnostic tool for thw diagnosis of pneumonia in the emergency department.
Emerg Med J 2012; 29 19-23.
F. Cortellaro et al.

Ciro Paolillo


  1. Hi brothers. In the last few months two important studies on lung ultrasound(LU) and pneumonia has been published, one by Coen & Duca, the other by Copetti & friends. The second study is really important because compares LU and 2 planes chest x-ray. LU combined with examination has an outstanding LR - 0.04. Do you think there is still place for the supine chest x-ray in diagnosing pneumonia? do you think is still usefull in excluding other causese of dyspnea or for legal issues? thanks for this magic blog

  2. Fisrt of all thank you for your comment!
    We think that if you can, you have to perform a 2 planes chest x ray (see also http://www.alifeatrisk.com/2012/06/chest-x-ray-and-aortic-dissection.html), but if the patient if unstable, to make a supine x ray is not a legal question, you need a panoramic view and above all an imagine that can go around with the patient…but you can't trust it if negative as you can't trust a 2 planes one as well! (see also http://www.alifeatrisk.com/2012/10/clinical-scenario-33-yo-woman-comes-to.html)