Risk assessment, testing and risk management form the very heart of Emergency Medicine and Critical Care. Being aware of the evidence surrounding a topic is key to delivering high level care but without an understanding of the underpinning concepts it's application is extremely limited. Understanding how a test result changes a patient's likelihood of a disease can be described with likelihood ratios, the Royal College of Emergency Medicine has a podcast explaining likelihood ratios in more detail. But when a test result comes back on the boundary between positive and negative, or at the extremes of positive we can find it difficult to know what this means and that's where interval likelihood ratios comes into play.  Examples include a minimally elevated WCC in a suspected appendicitis, or a dramatically raised d-dimer as compared to a borderline positive result in a suspected pulmonary embolus, this podcast talks through some of those concepts and their application, enjoy! References Evidence-based emergency medicine/skills for evidence-based emergency care. Interval likelihood ratios: another advantage for the evidence-based diagnostician. Brown MD. Ann Emerg Med. 2003 Pulmonary embolism: making sense of the diagnostic evaluation. Wolfe TR. Ann Emerg Med. 2001 Diagnostic accuracy of conventional or age adjusted D-dimer cut-off values in older patients with suspected venous thromboembolism: systematic review and meta-analysis. Schouten HJ. BMJ. 2013