We cover Dr. Rory Spiegel's blog EMNERD, covering an article in Chest 2015 by Pivetta et al, discussing the ways lung ultrasound (US) may be far more helpful than the brain natriuretic peptide (BNP) in determining heart failure in the dyspneic patient. 

Then we delve into likelihood ratios and show notes can be found at FOAMCAST.org

Bottom Line, LR of 1 is useless. It doesn't change the likelihood of using the disease.

+ LR >5 is good, + LR of 10 means that a test is useful and, if positive, patient most likely had the disease

- LR 0.2 is ok but a - LR of 0.1 is much more helpful.

Using a Fagan nomogran, one can understand how various likelihood ratios (and tests with their known LRs) may affect the post-test probability (i.e. the likelihood the patient has the disease). The utility of tests also depends on the pretest probability.