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 72 - Wellbeing with Liz Crowe
Ep - 71 SMACC Dublin Day 3 Round Up
Ep - 70 SMACC Dublin Day 2 Round Up.
Ep 69 - SMACC Dublin Day 1 Round Up
Ep 68 - An Englishman in South Africa with Robert Lloyd
Ep 67 - Intro to EM: Sepsis
Ep 66 - When Professional and Personal Worlds Collide with Liz Crowe
Ep 65 - The management of Paediatric trauma in the UK with Ross Fisher
Ep 64 - International Meeting for Simulation in Healthcarewith Sandra Viggers and Vic Brazil
Ep 63 - The Role of UK Trauma Units with Tim Coates (LTC)
Ep 62 - The role of paediatric surgeons in trauma with Ross Fisher (LTC)
Ep 61 - Grief at Christmas with Liz Crowe
Ep 61 - Londoon Trauma Conference 2015 Day 2 Summary
Ep 60 - Londoon Trauma Conference 2015 Day 1 Summary
Ep 59 - Lessons learned from the November Paris attacks with Youri Yordanov
Ep 58 - Clinical Judgement for the Emergency Physician
Ep 57 - When things go wrong - the difficult conversation
Ep 56 - Intro to EM: How to refer a patient
Ep 55 - Communicating (not Breaking) Bad News with Liz Crowe
Ep 54 - Intro to EM: Analgesia in the ED.
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