The latest CAN is one of our brand-new 'revision editions' -- brief podcasts aimed at covering the essentials of critical appraisal for medical students and junior doctors preparing for exams.
With the help of Gregory Yates, an academic doctor based in Manchester, this episode introduces two core concepts: sensitivity and specificity. These are two ways of thinking about the accuracy of a diagnostic test. Knowing the sensitivity and specificity of an investigation will give you a decent idea of how it should be used in the emergency department.
Sensitivity (Sn) describes the chance that a test will be positive if your patient has the condition you're testing for. Some people call it the 'true positive rate' or alternatively the positivity in disease (PID) rate. If you need a hand remembering it, you can always remember that PID is a sensitive issue.
Meanwhile, specificity (Sp) considers the chance of a test being negative if the patient doesn't have the condition you're testing for. It's the 'true negative rate' or alternatively the negativity in health (NIH) rate. There are times when we particularly need a test to have a high sensitivity. This is generally when we want to be particularly confident that a test accurately identifies everyone with the relevant condition because we really don't want to miss it. We need a high sensitivity to rule out disease. (Sn-uff it out). At other times, we need to be confident that a patient with a positive test actually has the disease - for example, if the treatment is unpleasant or involves exposing patients to risk. In that case, we want a high specificity to rule in disease. (Sp-in it in).
In this CAN, we use D-Dimer as an example of a very sensitive investigation: it’s positive in nearly 100% of cases of venous thromboembolism. Specificity describes the likelihood that the test will be negative if your patient does not have the disease. We use HbA1c as an example of a highly specific investigation: it’s rarely used in the emergency department, but if it’s elevated, we can be almost certain that the patient is diabetic. HbA1c is almost never (
Ep 111 - April 2018 Round Up
Ep 110 - March 2018 Round Up
Ep 109 - The Physican Response Unit (PRU) with Rich Carden and Tony Joy
Ep 108 - February 2018 Round Up
Ep 107 - January 2018 Round Up
Ep 106 - Debriefing in Critical Care with Liz Crowe
Ep 105 - Critical Apprasal Nugget 8: Diagnostics and PICTR questions.
Ep 104 - Managing Perceived Devastating Brain Injured patients with Dan Harvey and Mark Wilson
Ep 103 - December 2017 Round Up
Ep 102 - HEMS, reflections and St.Emlyn's e-books.
Ep 101 - November 2017 Round Up
Ep 100 - How to use WhatsApp and other group messaging systems in a Major Incident.
Ep 99 - October 2017 Round Up
Ep 98 - Life as an EM trainee in South Africa. A panel discussion
Ep 97 - Foreskins: A PED primer with Ross Fisher
Ep 96 - Everybody's free - Top Tips for the Class of 2017
Ep 95 - Non accidental injury in the ED.
Ep 95 - Burnout in Critical Care with Liz Crowe
Ep 94 - The Teaching Course Copenhagen Day 3
Ep 93 - The Teaching Course Copenhagen Day 2
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