Hot off the presses, JAMA just came out with a great Clinical Rational Examination article on this topic. Thanks to Dr. Ryan Radecki (EMLitOfNote) for the heads up. The likelihood ratios and Blatchford risk stratification score are so useful that I'm breaking my PV rule to keep things down to the size of one index card. Note the absence of a NG lavage result to help you risk stratify for an upper GI bleed requiring urgent intervention using the Blanchard score.
Let's say you have a patient with a Blanchard score of 0, as in the case of the JAMA example. Starting with a general 30% pretest probability that your upper GI bleed patient has a severe GI bleed, your post-test probability becomes <1% for a severe GI bleed.
These are pages 2 and 3 of my Upper GI Bleed PV card (June 2011), which was originally based on an EM Clinics of North America review article. View page 1.
Reference
Srygley FD, Gerardo CJ, Tran T, Fisher DA. Does this patient have a severe upper gastrointestinal bleed? JAMA. 2012 Mar 14;307(10):1072-9. Pubmed .